Self-induction-type position detector device for detecting object position

ABSTRACT

Single coil to be excited by a predetermined A.C. signal is provided, with no secondary coil being provided. Magnetism-responsive member is movable relative to the coil so that a self-inductance of the coil progressively increases or decreases in response to displacement of an object to be detected within a predetermined range and a voltage of the coil corresponding to the self-inductance is produced. Predetermined reference voltage is generated and subjected to analog operations with the coil output voltage, to thereby generate first and second A.C. outputs having, as amplitude coefficients, first and second cyclic amplitude functions correlated to the position to be detected. The position is detected on the basis of the phase component of the amplitude coefficient functions. Combination of two coils and one reference voltage may be employed. Further, a plurality of coil segments excitable by a same-phase signal are placed in series along the direction of displacement of the object so that a progressive increase or decrease occurs sequentially in the self-inductance of the coil segments as the magnetism-responsive member moves relative to the coil segments, and the voltage corresponding to the self-inductance is taken out from each of the coil segments. Performing analog arithmetic operations on combinations of the coil voltages produces first and second A.C. outputs having, as amplitude coefficients, first and second cyclic amplitude functions correlated to the position to be detected.

BACKGROUND OF THE INVENTION

The present invention relates to self-induction-type position detectordevices which include a coil to be excited by an A.C. signal and amagnetic or electrically-conductive member movable relative to the coiland which are suitable for detection of a linear or rotational position.More particularly, the present invention relates to an improvedself-induction-type position detector device which, in response to aposition of an object of detection (i.e., an object to be detected), cangenerate A.C. output signals presenting amplitude functioncharacteristics of a plurality of phases using only a primary coil to beexcited by a single-phase A.C. output signal.

There have ben known induction-type linear position detector deviceswhich are commonly called “LVDTs”. In two-wire-type LDVTs including oneprimary coil and one secondary coil, an induction coupling between theprimary coil and the secondary coils varies in accordance with an amountof entry, into a coil section, of a movable section made of a magneticsubstance, so that an inductive output signal of a voltage levelcorresponding to the induction coupling variation is produced in thesecondary coil. Further, three-wire-type LDVTs are constructed as adifferential transformer including one primary coil and two secondarycoils connected in series in opposite phases, where an inductioncoupling between the primary coil and the secondary coils varies in abalanced manner in accordance with an amount of entry, into one of thetwo coils of the opposite phases, of a movable section made of amagnetic substance having a predetermined length, so that inductiveoutput signals of voltage levels corresponding to the induction couplingvariation are produced in the secondary coils. In such three-wire-typeLDVTS, output signals of sine and cosine characteristics correspondingto a position of the movable section are generated by performing analogaddition or subtraction on the output signals from the secondary coils,and these output signals of sine and cosine characteristics are thenprocessed via an R-D converter to thereby generate digital dataindicative of a detected current position of the movable section. Othertype of position detector device have also been known (e.g., fromJapanese Patent Laid-open Publication No. SHO-53-102070 and U.S. Pat.No. 4,112,365 corresponding thereto), which include only an excitingcoil and where a variation in the self-inductance of the exciting coilresponding to a movement of a movable magnetic core is detected bymeasuring an amount of phase shift through an R-L circuit.

However, because the conventionally-known LVDTs require both of theprimary and secondary coils, the necessary number of component partswould increase, which unavoidably results in significant limits toreduction in the manufacturing cost and size of the devices. Inaddition, an available phase angle range in the output signals of sineand cosine characteristics corresponding to a current position of themovable section is relatively narrow, such as about 45° in thetwo-wire-type LVDTs or about 90° in the three-wire-type LVDTs, so thatthe detectable phase angle range can not be expanded satisfactorily inthe conventionally-known LVDTs. Further, because the conventionalthree-wire-type LVDTs can only detect such positions displaced leftwardand rightward from a predetermined reference point where the movablesection is located centrally along the length the coil section, theyprovide a very poor convenience of use.

With the conventionally-known position detector devices of the typewhich measures the self-inductance of the exciting coil, on the otherhand, it is possible to reduce the necessary number of coils, but thephase shift amount responding to the displacement of the object to bedetected can be detected only within an extremely narrow range, which,in effect, would make it very difficult to measure the phase shiftamount. Also, these known position detector devices provide a very poordetecting resolution and thus are not suitable for practical use. Inaddition, because the phase shift amount varies as the impedance of thecoil changes in response to a change in ambient temperature, theposition detector devices could not properly compensate or adjust theirtemperature characteristics.

Induction-type rotational position detector devices of the type whichproduces two-phase outputs (i.e., outputs of sine and cosine phases) inresponse to a single-phase exciting input are commonly known as“resolvers”, and induction-type rotational position detector devices ofthe type which produces three-phase outputs (i.e., outputs of threephases shifted from each other by 120°) in response to a single-phaseexciting input are commonly known as “synchros”. In the resolvers in themost traditional form, a stator includes two-pole (sine and cosinepoles) secondary windings that intersect each other at a 90° mechanicalangle, and a rotor includes a primary winding. The resolvers of thistype are not satisfactory in that they need a brush to electricallycontact the primary winding of the rotor. There have also been knownbrush-less resolvers that require no such brush; that is, thesebrush-less resolvers include, in the rotor, a rotary transformer inplace of the brush. However, because of the provision of the rotarytransformer in the rotor, it is difficult to reduce the overall size ofthe devices and thus there are limitations to the downsizing of thebrush-less resolvers. Further, the provision of the rotary transformerincreases the number of the component parts, which also leads to anunavoidable increase in the manufacturing cost.

Also known in the art are rotational position detector devices of thenon-contact/variable-reluctance type (known in the past by the tradename“microsyn”), where a stator includes primary and secondary windingsdisposed on a plurality of projecting poles and a rotor is formed of amagnetic body having a predetermined shape (such as an eccentriccircular shape, an oval shape or a shape having a projection). In theserotational position detector devices (rotary-type position detectordevices), a reluctance variation responding to a rotational position ofthe object to be detected is produced on the basis of variations in gapsbetween the stator's projecting poles and the rotor's magnetic body thatoccur in response to a changing rotational position of the object to bedetected, so that an output signal corresponding to the reluctancevariation is provided. Further, similar reluctance-based rotationalposition detector devices are also disclosed, for example, in U.S. Pat.No. 4,754,220, Japanese Patent Laid-open Publication Nos. SHO-55-46862,SHO-55-70406 and SHO-59-28603. As position detection techniques based onthe detector output signal, there have been known both a phase-basedscheme in which position detecting data corresponds to an electricalphase angle of the output signal and a voltage-based scheme in whichposition detecting data corresponds to a voltage level of the outputsignal. In the case where the phase-based scheme is employed, theindividual primary windings disposed at different mechanical angles areexcited by phase-shifted inputs, such as two-phase or three-phaseexciting inputs, so as to generate a single-phase output signal having adifferent electrical angle corresponding to a current rotationalposition. Further, in the case where the voltage-based scheme isemployed, the relationship between the primary and secondary windings isreversed from that in the phase-based scheme, and plural-phase outputsare produced in response to a single-phase exciting input in the samemanner as in the resolvers.

Typically, the rotational position detector devices, such as theresolvers, which produce plural-phase outputs in response to asingle-phase, are arranged to produce two-phase outputs, namely,sine-phase and cosine-phase outputs. To this end, in the conventionalresolver-style rotational position detector devices of thenon-contact/variable-reluctance type, the stator has at least four polesthat are spaced apart from each other by a mechanical angle of 90°;specifically, if the first pole is set to a sine phase, the second pole90° apart from the first pole is set to a cosine phase, the third pole90° apart from the second pole is set to a minus sine phase and thefourth pole 90° apart from the third pole is set to a minus cosinephase. In such a case, to bring about a reluctance variation,corresponding to a rotation of the object to be detected, in each of thestator poles, the rotor is formed of a magnetic orelectrically-conductive substance into an eccentric circular shape, ovalshape or cyclic shape such as a gear shape. Primary and secondarywindings are disposed on each of the stator poles so that a reluctancein a magnetic circuit passing through the stator pole is changed inresponse to a variation in a gap between the stator pole and therotator. The reluctance change causes a degree of magnetic couplingbetween the primary and secondary coils on each of the stator poles tovary in correspondence with a rotational position of the object to bedetected, and thus an output signal corresponding to the rotationalposition is induced in each of the secondary winding, with the resultthat a peak amplitude characteristic in the output signal from each ofthe stator poles presents a cyclic function characteristic.

However, because the above-discussed resolver-style rotational positiondetector devices of the non-contact/variable-reluctance type are basedon primary-secondary induction by the provision of the primary andsecondary coils, a great number of coils are required, which wouldunavoidably result in limits to reduction in the manufacturing cost andoverall size of the devices. Further, with the arrangement that theplurality of stator poles are disposed at equal intervals along theentire range of one full rotation, the conventional rotational positiondetector devices would present the problem that places and space towhich the devices are applicable are limited to a considerable degree.Besides, even where two-phase (sine-phase and cosine-phase) outputs areto be produced from the conventional rotational position detectordevices, the stator can not be constructed as a simple two-polestructure and always has to be constructed as a more complicatedfour-pole structure, which would also impose limitations to reduction inthe overall size of the stator.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved position detector device which is very compact in size and verysimple in structure. It is another object of the present invention toprovide an improved position detector device which achieves asignificant increase in its available phase angle range, can accuratelydetect even microscopic displacement of an object to be detected withhigh resolution and also can readily compensate its temperaturecharacteristics in an appropriate manner.

In order to accomplish the above-mentioned object, the present inventionprovides a position detector device which comprises: a coil sectionincluding at least one coil to be excited by an A.C. signal; amagnetism-responsive member movable relative to said coil section,wherein relative positions between said magnetism-responsive member andsaid coil section vary in response to displacement of an object to bedetected and impedance of said coil is caused to vary in response to avariation in the relative positions in such a manner that a voltageproduced in said coil is caused to vary in response to a variation inthe impedance of said coil during the variation in the relativepositions within a predetermined range; a reference-voltage generationcircuit adapted to generate at least one predetermined reference voltagein the form of an A.C. signal; and an arithmetic operation circuitcoupled to said coil and reference-voltage generation circuit, saidarithmetic operation circuit adapted to perform an arithmetic operationbetween said voltage produced in said coil and said predeterminedreference voltage, so as to generate at least two A.C. output signalshaving predetermined cyclic amplitude functions as amplitudecoefficients, the cyclic amplitude functions of the two A.C. outputsignals being different, in their cyclic characteristics, from eachother by a predetermined phase.

Typically, the magnetism-responsive member includes at least one of amagnetic substance and an electrically-conductive substance. In the casewhere the magnetism-responsive member is made of a magnetic substance,the inductance and electrical impedance of the coil increases and thevoltage produced in the coil, i.e., a voltage between two terminals(i.e., “between-terminal voltage”) of the coil, increases as themagnetism-responsive member moves closer to the coil, i.e., as thedegree of proximity of the magnetism-responsive member to the coilincreases. Conversely, as the magnetism-responsive member moves awayfrom the coil, i.e., as the degree of proximity of themagnetism-responsive member to the coil decreases, the inductance andelectrical impedance of the coil decreases and the voltage produced inthe coil, i.e., “between-terminal voltage” of the coil, decreases. Thus,in response to displacement (changing position) of the object to bedetected, the between-terminal voltage of the coil increases ordecreases as the relative position of the magnetism-responsive member tothe coil varies within a predetermined range.

Typically, a progressive variation curve of the between-terminal voltageof the coil, presented during the movement of the magnetism-responsivemember relative to the coil, can be likened to a functional valuevariation within a 0°-90° range of a sine function. If an A.C. signalcomponent is represented by “sin ωt” and an amplitude coefficient levelof the output voltage Vx of the coil obtained in correspondence with thestart point of an appropriate detection section in the progressivevariation curve presented by the between-terminal voltage of the coil isrepresented by “Pa”, the output voltage Vx from the coil correspondingto the start point of the detection section can be represented by “Pasin ωt”. Similarly, if an amplitude coefficient level of the outputvoltage Vx of the coil obtained in correspondence with the end point ofthe above-mentioned detection section in the progressive variation curveis represented by “Pb”, then the coil output voltage corresponding tothe end point of the detection section can be represented by “Pb sinωt”. Further, if an A.C. voltage having the same value as the value Pasin ωt of the coil output voltage Vx corresponding to the start point ofthe detection section is set as a reference value Va and the amplitudecoefficient of the coil output voltage Vx is represented by A(x),subtracting the first reference voltage Va from the coil output voltageVx gives the following mathematical expression:

Vx−Va=A(x)sin ωt−Pa sin ωt={A(x)−Pa}sin ωt  Expression(1)

Because A(x) equals Pa at the start point of the detection section, theamplitude coefficient “A(x)−Pa”, which is the result of these arithmeticoperations, becomes “0”. On the other hand, at the end point of thedetection section, A(x) equals Pb, so that the amplitude coefficient“A(x)−Pa”, which is the result of these arithmetic operations, equals“Pb−Pa”. Thus, the “A(x)−Pa”, the result of these arithmetic operations,presents a function characteristic increasing progressively from “0” to“Pb−Pa”. If the maximum value “Pb−Pa” is regarded equivalently as “1”,then the amplitude coefficient “A(x)−Pa” of the A.C. signal based onExpression (1) above varies from “0” to “1” within the detectionsection, and the function characteristic of the amplitude coefficientcan be likened to a characteristic of a first quadrant (i.e., a 0°-90°range) in a sine function. Therefore, the amplitude coefficient“A(x)−Pa” of the A.C. signal based on the above mathematical expressioncan be expressed equivalently as sin θ (approximately, 0°≦θ≦90°).

In a preferred implementation of the position detector device, the coilsection includes a single coil, and the reference-voltage generationcircuit generates first and second reference voltages. The arithmeticoperation circuit performs predetermined first and second arithmeticoperations using a voltage taken out from the single coil and the firstand second reference voltages, to thereby generate a first A.C. outputsignal having a first amplitude function as an amplitude coefficient anda second A.C. output signal having a second amplitude function as anamplitude coefficient. In this case, the position detector devicerequires only one coil and thus can be as simple as possible instructure. Further, using the voltage Va as the above-mentioned firstreference voltage, the above-mentioned first amplitude function can havea characteristic corresponding generally to the first quadrant (i.e.,the 0°-90° range) in the sine function.

If an A.C. voltage having the same value as the value Pb sin ωt of thecoil output voltage Vx corresponding to the end point of the detectionsection is set as a second reference value Vb, subtracting the secondreference voltage Vb from the coil output voltage Vx gives the followingmathematical expression:

Vb−Vx=Pb sin ωt−A(x)sin ωt={Pb−A(x)}sin ωt  Expression (2)

Because A(x) equals Pa at the start point of the detection section, theamplitude coefficient “Pb−A(x)”, which is the result of these arithmeticoperations, equals “Pb−Pa”. On the other hand, at the end point of thedetection section, A(x) equals Pb, so that the amplitude coefficient“Pb−A(x)”, which is the result of these arithmetic operations, becomes“0”. Thus, the “Pb−A(x)”, the result of these arithmetic operations,presents a function characteristic decreasing progressively from “Pb−Pa”to “0”. If the maximum value “Pb−Pa” is regarded equivalently as “1”,then the amplitude coefficient “Pb−A(x)” of the A.C. signal based onExpression (2) above varies from “1” to “0” within the detectionsection, and the function characteristic of the amplitude coefficientcan be likened to a characteristic of a first quadrant (i.e., a 0°-90°range) in a cosine function. Therefore, the amplitude coefficient“Pb−A(x)” of the A.C. signal based on Expression (2) can be expressedequivalently as cos θ (approximately, 0°≦θ≦90°). The subtraction inExpression (2) may be replaced by “Vx−Vb”.

In the above-mentioned manner, by only using a combination of one coiland two reference voltages, the present invention can readily producetwo A.C. output signals presenting amplitudes of sine and cosinefunction characteristics, in response to a current position of theobject to be detected. For example, if the position of the object to bedetected is represented by an angle θ, then the A.C. output signalpresenting an amplitude of a sine function characteristic can beexpressed by sin θ sin ωt while the A.C. output signal presenting anamplitude of a cosine function characteristic can be expressed by cos θsin ωt. These output signals are just similar in form to the outputsfrom the known position detector devices commonly called “resolvers”,which are therefore extremely useful in various applications. In someapplication, the inventive position detector device may further comprisean amplitude-to-phase converter section that receives the plurality ofA.C. output signals generated via the above-mentioned arithmeticoperation circuit, then detects, from a correlation between theamplitude values of the A.C. output signals, a specific phase value inthe sine and cosine functions defining the amplitude values, and thengenerates position detecting data indicative of a current position ofthe object to be detected. Note that because the sine and cosinefunctions each present a characteristic within a range of substantiallyone quadrant (90°), every position over a detectable position range canbe detected in terms of a phase angle within the substantially-90°range.

In this case, variably setting the levels Pa and Pb of the referencevoltages Va and Vb would result in variably setting the detectableposition range of the device. If the levels Pa and Pb of the referencevoltages Va and Vb are set to be greatly different from each other, thenthe detectable position range will be widened accordingly, while if thelevels Pa and Pb of the reference voltages Va and Vb are set to be onlyslightly different from each other, then the detectable position rangewill be narrowed. Because any position within the detectable positionrange can always be detected in terms of a phase angle θ within thesubstantially-90° range irrespective of a change in the detectableposition range, the detecting resolution of the inventive positiondetection can be variably set by just variably setting the levels of thereference voltages Va and Vb. This means that the position detection canbe made with a super-high resolution even where very minute ormicroscopic displacement of the object is to be detected.

In another preferred embodiment, the coil section includes two coils,relative positions of the two coils relative to the magnetism-responsivemember being caused to vary with opposite characteristics in response tothe displacement of the object to be detected, in response to whichrespective impedance of the coils varies with opposite characteristics.In this case, the reference-voltage generation circuit generates asingle reference voltage, and the arithmetic operation circuit performspredetermined first and second arithmetic operations using voltagestaken out from the coils and the reference voltage, to thereby generatea first A.C. output signal having a first amplitude function as anamplitude coefficient and a second A.C. output signal having a secondamplitude function as an amplitude coefficient.

Similarly to the above-mentioned, a progressively increasing variationcurve of the between-terminal voltage of the first coil, presentedduring a variation of the relative position of the magnetism-responsivemember within a predetermined range, can be likened to a functionalvalue variation in a 0°-90° range of a sine function. Namely, the outputvoltage Vx from the coil corresponding to the start point of anappropriate detection section can be represented by Pa sin ωt, whichcorresponds to a minimum voltage value. The start point of the detectionsection can be set by the reference voltage Va. Performing arithmeticoperations similar to Equation (1) above using the reference voltage Va(=Pa sin ωt) gives

Vx−Va={A(x)−Pa}sin ωt

As in the above-mentioned case, the function characteristic of theamplitude coefficient “A(x)−Pa” can be likened to a characteristic ofthe first quadrant (i.e., the 0°-90° range) in a sine function, namely,it can be expressed equivalently as sin θ (approximately, 0°≦θ≦90°).

On the other hand, the second coil in the coil section presents aprogressively decreasing variation curve opposite to the curve of thefirst coil. The output voltage Vy from the second coil corresponding tothe start point of the detection section can be representedprovisionally by “Pa′ sin ωt”, which corresponds to a maximum voltagevalue. Subtracting the reference voltage Va from the second coil outputvoltage Vy gives the following mathematical expression where theamplitude coefficient of the output voltage Vy is represented by A(y):

Vy−Va=A(y)sin ωt−Pa sin ωt={A(y)−Pa}sin ωt  Expression (3)

Because A(y) equals Pa′ at the start point of the detection section, theamplitude coefficient “A(y)−Pa”, which is the result of the arithmeticoperations, equals “Pa′−Pa” representing “maximum value−minimum value”,which therefore becomes a maximum value that can be regardedequivalently as “1”. At the end point of the detection section, on theother hand, A(y) equals Pa, so that the amplitude coefficient “A(y)−Pa”,the result of the above arithmetic operations, becomes “0”. Thus, theamplitude coefficient “A(y)−Pa” presents a function characteristicprogressively decreasing from the maximum value “Pa′−Pa” (namely, “1”)to “0” within the range of the detection section. This functioncharacteristic of the amplitude coefficient can be likened to acharacteristic of the first quadrant (i.e., the 0°-90° region) in thecosine function. Therefore, the amplitude coefficient “A(y)−Pa” of theA.C. output signal based on Expression (3) above can be expressedequivalently as cos θ (approximately, 0°≦θ≦90°).

Thus, in the case where a combination of two coils and a singlereference voltages is employed as above, the present invention canreadily produce two A.C. output signals presenting amplitudes of sineand cosine function characteristics (sin θ sin ωt and cos θ sin ωt), inresponse to a current position of the object to be detected. In thiscase too, the sine and cosine functions each present a characteristicwithin a range of substantially one quadrant (90°), so that everyposition over a detectable position range can be detected in terms of aphase angle within the substantially-90° range. Further, by justvariably setting the level of the reference voltage Va, the detectableposition range can be variably set and the detecting resolution of thedevice can be adjusted as desired, similarly to the above-mentioned.

Thus, according to the present invention, there can provide an improvedposition detector device which is very compact in size and very simplein structure, because it requires only a primary coil (or coils) with noneed for a secondary coil. Further, using a combination of one coil andtwo reference voltages or a combination of two coils and one referencevoltage, the present invention can readily produce a plurality of A.C.output signals presenting amplitudes of predetermined cyclic functioncharacteristics (e.g., two A.C. output signals presenting amplitudes ofsine and cosine function characteristics), in response to a currentlinear position of the object to be detected, and also can provide atleast about one quadrant (90°) as an available phase angle range. Thus,even with a reduced number of coils, the present invention is capable ofeffective position detection over a relatively wide phase angle rangeand also achieves a highly enhanced detecting resolution. Besides, evenfor very minute or microscopic displacement of the object to bedetected, the present invention allows a position of the object to bedetected with a high resolution. Furthermore, by employing a circuit(e.g., a coil) presenting temperature characteristics similar to thoseof the detecting coils as the reference-voltage generation circuit,predetermined subtractive arithmetic operations in arithmetic operationcircuitry can automatically compensate the temperature driftcharacteristics in an appropriate manner, thereby providing forhigh-accuracy position detection without influences of a temperaturechange. Further, to construct the reference-voltage generation circuit,a resistor or other suitable element may be used in place of the coils.Furthermore, the numbers of the coil and reference voltage may begreater than one or two, in which case the available phase angle rangemay be expanded to be greater than about one quadrant (90°).

The position detector device of the present invention can also beconstructed as a rotary-type position detector device. If the amplitudecoefficient component produced by an incremental (increasing) ordecremental (decreasing) variation in the between-terminal voltage of acoil, corresponding to a rotational displacement of the object to bedetected is represented by a function A(θ) with a rotational angle e asa variable, the between-terminal voltage of the coil can be expressed byA(θ)sin ωt. In this case, the amplitude coefficient component A(θ) takesonly a positive value although it increases or decreases in accordancewith the rotational displacement of the object to be detected. Assumingthat the incremental/decremental variation curve of the amplitudecoefficient component A(θ) presents a characteristic approximate to thatof a sine curve and if its peak value is denoted by P, the amplitudecoefficient component A(θ) can be expressed typically by an equation of“A(θ)=Po+P sin θ”, where Po≧P. Namely, the amplitude coefficientcomponent A(θ) presents such a characteristic that is obtainable byoffsetting the value of P sin θ with the offset value Po.

The rotary-type position detector device of the present invention ischaracterized by: generating a predetermined reference voltage; takingout a voltage between terminals of a coil; and performing an arithmeticoperation between the predetermined reference voltage and the taken-outbetween-terminal voltage of the coil, so as to generate an A.C. outputsignal having a predetermined cyclic amplitude function as an amplitudecoefficient. If the predetermined reference voltage is represented by Posin ωt, subtracting the reference voltage Po sin ωt from thebetween-terminal voltage of the coil A(θ)sin ωt gives

A(θ)sin ωt−Po sin ωt=(Po+Po sin θ)sin ωt−Po sin ωt=Po sin θ sin ωt

By performing arithmetic operations between the output signal from thesingle coil and the reference voltage, there can be generated an A.C.output signal having an amplitude coefficient component of a real sinefunction sine (or real cosine function) swinging in the positive andnegative directions. Such inventive arrangements can greatly simplifythe necessary coil structure. Further, the present invention can providean improved rotary-type position detector device which is event morecompact in size and even simpler in structure, because it requires onlya primary coil with no need for a secondary coil.

In one embodiment of the inventive rotary-type position detector device,the coil section includes two coils positioned to be apart from eachother by a predetermined angle along a direction of variation ofrelative rotational positions between the coils and themagnetism-responsive member, and the reference-voltage generationcircuit generates a reference voltage (e.g., Po sin ωt) corresponding toa center point of variation in a voltage between terminals of each ofthe two coils. The arithmetic operation circuit subtracts the referencevoltage from the voltage between the terminals of a first one of the twocoils to cancel out a voltage offset corresponding to the referencevoltage and thereby generates a first A.C. output signal (e.g., sin θsin ωt) having, as an amplitude coefficient, a first cyclic amplitudefunction swinging about the center point of variation in positive andnegative directions. The arithmetic operation circuit also subtracts thereference voltage from the voltage between the terminals of a second oneof the two coils to cancel out a voltage offset corresponding to thereference voltage and thereby generates a second A.C. output signal(e.g., cos θ sin ωt) having, as an amplitude coefficient, a secondcyclic amplitude function swinging about the center point of variationin the positive and negative directions. In this case, by providing onlytwo coils, there can be generated a sine-phase output signal (sin θ sinωt) and a cosine-phase output signal (cos θ sin ωt) similar to thoseproduced by the known resolvers.

In another embodiment of the inventive rotary-type position detectordevice, the arithmetic operation circuit performs predetermined firstand second arithmetic operations using the voltage between the terminalsof one of the coils and the reference voltage, to thereby generate afirst A.C. output signal having a first amplitude function as itsamplitude coefficient and a second A.C. output signal having a secondamplitude function as its amplitude coefficient. In this case,respecting a rotational displacement of the object within apredetermined limited range of mechanical rotational angles, positiondetecting data can be obtained on a predetermined limited phasedetecting scale (i.e., a 90° range) rather than a full 360° phasedetecting scale, as will be later described more fully. Despite thepredetermined limited phase detecting scale, there can be generated asine-phase output signal (sin θ sin ωt) and cosine-phase output signal(cos θ sin ωt) similar to those produced by the known resolvers, usingonly one coil.

In another implementation of the inventive rotary-type position detectordevice, the coil section may be provided in a predetermined limitedangular range less than one full rotation range of the object to bedetected so that the detector device can be suitably used to detect arotational position within the predetermined limited angular range. Sucha coil section extending only over a limited or biased angular rangewill be useful particularly in a situation where the rotary-typeposition detector device of the present invention is to be installed ina previously installed machine or apparatus. Namely, where some largeobstacle is already present within the predetermined rotating anglerange of an rotation shaft, which is the object to be detected, and itis impossible to install the stator coil section over a rangecorresponding to the full rotation of the rotation shaft, the coilsection extending only over the limited angular range in the embodimentcan be readily installed in an obstacle-free angular range, and thus canbe very useful.

A rotary-type position detector device according to another aspect ofthe present invention comprises: a coil section including at least twopairs of coils to be excited by an A.C. signal, the coils in each of thepairs being positioned to be apart from each other by a distancecorresponding to a predetermined rotational angle; amagnetism-responsive member rotationally movable relative to said coilsection, wherein relative rotational positions between saidmagnetism-responsive member and said coil section vary in response torotational displacement of an object to be detected and impedance ofeach of said coils is caused to vary in response to a variation in therelative rotational positions in such a manner that a voltage producedin each of said coils is caused to vary in response to a variation inthe impedance of said coil during the variation in the relativerotational positions within a predetermined rotational angle range, thevoltages produced in the respective coils in each of the pairspresenting differential characteristics; and a circuit coupled to saidcoil section, said circuit adapted to generate, for each of said twopairs of coils, an A.C. output signal having a predetermined cyclicamplitude function as an amplitude coefficient, by taking out adifference in the voltages produced in said respective coils, the cyclicamplitude functions of the A.C. output signals generated for said twopairs of coils being different in their cyclic characteristics by apredetermined phase.

If one of the coil pairs in the thus-constructed rotary-type positiondetector device is be of a sine phase and if one of the coils in thepair presents a characteristic of (Po+Po sin θ)sin ωt, then the othercoil in the pair presents a characteristic of (Po−Po sin θ)sin ωt,because the incremental/decremental variations in the produced voltages,i.e., between-terminal voltages, of the coils in that pair presentdifferential characteristics. Thus, taking out a difference between thetwo characteristics gives

(Po+P sin θ)sin ωt−{(Po−P sin θ))sin ωt}=2P sin θ sin ωt

Further, If the other coil pair in this inventive rotary-type positiondetector device is be of a cosine phase, the incremental/decrementalvariations in the between-terminal voltages of the coils in that pairpresent differential characteristics as follows. Namely, taking out adifference between the two characteristics gives

(Po+P cos θ)sin ωt−{(Po−P cos θ)sin ωt}=2P cos θ sin ωt

Such a different ial synthesis principle employed in the presentinvention is generally similar to the one already known in the field ofthe resolvers, except that the conventional-known resolvers wouldrequire both primary and secondary coils. Namely, in contrast to theconventional-known resolvers, the present invention requires onlyprimary coils with no need for any secondary coil and thus can simplifythe necessary coil structure, with the result that there can be providedan improved rotary-type position detector device significantlysimplified in structure.

A position detector device according to still another aspect of thepresent invention comprises: a coil section including a plurality ofcoil segments to be excited by a predetermined A.C. signal, the coilsegments being placed in series along a direction of displacement of anobject to be detected; a magnetism-responsive member movable relative tosaid coil section, wherein relative positions between saidmagnetism-responsive member and said coil section vary in response todisplacement of the object to be detected and impedance of each of saidcoil segments is caused to vary in response to a variation in therelative positions in such a manner that a voltage produced in each ofsaid coil segments is caused to progressively increase or decreaseduring a movement of said magnetism-responsive member from one end toanother of each of said coil segments; and an analog arithmeticoperation circuit coupled to said coil section, said analog arithmeticoperation circuit adapted to generate a plurality of A.C. output signalspresenting amplitudes based on predetermined cyclic functioncharacteristics corresponding to a position of the object to bedetected, by taking out voltages of said coil segments and performingaddition and/or subtraction on the taken-out voltages, the cyclicfunction characteristics defining the amplitudes of the plurality ofA.C. output signals comprising cyclic functions of a same character thatare different from each other by a predetermined phase.

Typically, the magnetism-responsive member includes at least one of amagnetic substance and an electrically-conductive substance. In the casewhere the magnetism-responsive member is made of a magnetic substance,as the magnetism-responsive member moves closer to any one of the coilsegments, i.e., as the degree of proximity of the magnetism-responsivemember to the coil segments increases, the self-inductance of the coilsegment increases and the voltage produced in the coil segment (i.e., abetween-terminal voltage of the coil segment) progressively increasesduring a movement of the tip of the magnetism-responsive member from oneend to the other of the coil segment. By the sequential placement of theplurality of coil segments along the direction of displacement of theobject to be detected, a progressive increase (or progressive decrease)occurs sequentially in the between-terminal voltages of the coilsegments as the magnetism-responsive member moves relative to these coilsegments in response to the displacement of the object to be detected.Thus, by combining and using the progressive increases (or progressivedecreases) in the between-terminal voltages of the individual coilsegments while regarding them as variations in partial phase ranges ofpredetermined cyclic functions, the present invention can generate aplurality of A.C. output signals presenting amplitudes based onpredetermined cyclic function characteristics corresponding to a currentposition of the object to be detected. Namely, the plurality of A.C.output signals presenting amplitudes based on predetermined cyclicfunction characteristics, corresponding to a position of the object tobe detected, can be generated by taking out the between-terminalvoltages of the coil segments and performing addition and/or subtractionon the taken-out voltages.

Typically, a progressively-increasing variation curve of thebetween-terminal voltage of any one of the coil segments, which takesplace during the movement of the magnetism-responsive member from thecoil's one end to the other, can be likened, for example, to afunctional value variation over a 0°-90° range of a sine function.Further, this progressively-increasing variation curve can be convertedinto a variation curve progressively decreasing from a predeterminedlevel, by inverting the amplitudes of the voltages and performing avoltage shift operation to add a predetermined offset level to theinverted amplitudes. Such a progressively-decreasing variation curve ofthe between-terminal voltage can be likened, for example, to afunctional value variation over a 90°-180° range of a sine function.Thus, the progressively-increasing variations of the between-terminalvoltage, sequentially occurring, for example, in a series of four coilsegments, can be likened to function value variations in the 0°-90°range, 90°-180° range, 180°-270° range and 270°-360° range,respectively. Sloping direction and voltage-shifting offset level ineach of these ranges can be controlled as appropriate through suitableanalog arithmetic operations. Thus, the present invention can generate afirst A.C. output signals presenting amplitudes based on the sinefunction characteristic corresponding to a position of the object to bedetected, as well as a second A.C. output signals presenting amplitudesbased on the same-character cyclic function, i.e., the cosine functioncharacteristic, which is shifted in phase from the sine function by 90°.

Thus, as a preferred embodiment of the present invention, there can begenerated two A.C. output signals presenting amplitudes based on thesine and cosine function characteristics corresponding to a currentposition of the object to be detected. Generally, the A.C. outputsignals having amplitudes based on the sine function characteristic canbe represented by sinesinot, while the A.C. output signals havingamplitudes based on the cosine function characteristic can berepresented by cos θ sin ωt. These output signals are just similar inform to the outputs from the known position detector devices commonlycalled “resolvers”, which are therefore extremely useful in variousapplications. In some application, the inventive position detectordevice may further comprise an amplitude-to-phase converter section thatreceives two A.C. output signals generated via the above-mentionedanalog arithmetic operation circuit, then detects, from a correlationbetween the amplitude values of the A.C. output signals, a specificphase value in the sine and cosine functions defining the amplitudevalues, and then generates position detecting data indicative of acurrent position of the object to be detected.

Thus, according to the present invention, there can be provided animproved position detector device which is very compact in size and verysimple in structure, because it requires only a primary coil with noneed for any secondary coil. In addition, with the arrangement that aplurality of coil segments are placed in series along the direction ofdisplacement of the object to be detected so that a progressive increase(or progressive decrease) occurs sequentially in the between-terminalvoltages of the coil segments as the magnetism-responsive member movesfrom one end to the other of any one of the coil segments, the presentinvention can readily produce a plurality of A.C. output signalspresenting amplitudes of predetermined cyclic function characteristics(e.g., two A.C. output signals presenting amplitudes of sine and cosinefunction characteristics), in response to a current linear position ofthe object to be detected, by taking out the between-terminal voltagesof the coil segments and combining the taken-out voltages afterperforming addition and/or subtraction thereon. Further, the presentinvention can provide a wider available phase angle range; for example,the invention is also cable of detecting positions over a full phaseangle range of 0°-360°. Because the plurality of A.C. output signalspresenting amplitudes of predetermined cyclic function characteristicsare generated by combining the output voltages from the plurality ofcoil segments presenting the same temperature characteristics afteraddition or subtraction having been performed thereon, the presentinvention can automatically compensate the temperature characteristicsin an appropriate manner, thereby readily providing for high-accuracyposition detection without influences of a temperature change. Inaddition, even for very minute or microscopic displacement of the objectto be detected, a current position of the object can be detected with ahigh resolution, by detecting, from a correlation between the amplitudevalues of these A.C. output signals, a phase value in the predeterminedcyclic functions (e.g., sine and cosine functions) defining theamplitude values.

Note that in the case where the magnetism-responsive member is made of anon-magnetic substance of good electrical conductivity, such as copper,there occurs an eddy-current loss that causes the self-inductance of thecoil to decrease and the between-terminal voltage of the coilprogressively decreases as the magnetism-responsive member moves closerto the coil. In this case too, the position detector device may beconstructed in the same manner as mentioned above. Also, it is importantto note that the magnetism-responsive member may be of a hybrid typecomprising a combination of a magnetic substance and anelectrically-conductive substance. As another example, themagnetism-responsive member may include a permanent magnet and the coilsection may include a magnetic core. In this case, as the permanentmagnet approaches, a corresponding portion of the magnetic core in thecoil section is magnetically saturated or super-saturated, so that thebetween-terminal voltage of the coil progressively decreases in responseto the movement of the magnetism-responsive member closer to the coil.Further, dummy impedance means, namely, the reference-voltage generationcircuit, may comprise a resistor or inductance means such as a coil, asnoted previously; however, the dummy coil has to be positioned in such amanner that its self-inductance is not influenced by the movement of themagnetism-responsive member.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the object and other features of the presentinvention, its preferred embodiments will be described in greater detailhereinbelow with reference to the accompanying drawings, in which:

FIG. 1A is a schematic axial sectional view showing a principal part ofa position detector device in accordance with an embodiment of thepresent invention, which is taken along an axis of a coil section;

FIG. 1B is a schematic plan view of the part of the position detectordevice shown in FIG. 1A;

FIG. 1C is a block diagram showing electric circuitry associated withthe coil section of FIG. 1A;

FIGS. 2A and 2B are graphs explanatory of position detecting operationof the embodiment shown in FIG. 1A;

FIG. 3A is a schematic axial sectional view showing a principal part ofa modification of the position detector device shown FIGS. 1A and 1B;

FIG. 3B is a schematic plan view of the part of the position detectordevice shown in FIG. 3A;

FIG. 4 is a schematic axial sectional view showing a principal part ofanother modification of the position detector device shown FIGS. 1A and1B;

FIG. 5 is a schematic axial sectional view showing a principal part ofstill another modification of the position detector device shown FIGS.1A and 1B;

FIG. 6 is a schematic axial sectional view showing a principal part ofstill another modification of the position detector device shown FIGS.1A and 1B;

FIG. 7A is a schematic axial sectional view showing a principal part ofa position detector device in accordance with another embodiment of thepresent invention;

FIG. 7B is a block diagram showing electric circuitry associated with acoil section of FIG. 7A;

FIGS. 8A and 8B are graphs explanatory of position detecting operationof the embodiment shown in FIG. 7A;

FIGS. 9A-9C show a rotary-type position detector device in accordancewith an embodiment of the present invention, of which FIG. 9A is aschematic front view of a principal part of the position detector deviceshowing an example of a physical positional relationship betweenindividual detecting coils of a stator section and a magnetic-responsivemember of a rotor section in the position detector device, FIG. 9B is aschematic sectional side view of the part of the position detectordevice, and FIG. 9C is a block diagram showing an example of electriccircuitry associated with the detecting coils of the stator section;

FIGS. 10A and 10B are graphs explanatory of position detecting operationof the embodiment shown in FIGS. 9A to 9C, of which FIG. 10A shows idealcurves of impedance variations of the individual detecting coilsresponding to a variation in a rotational angle θ, FIG. 10B showsamplitude variation characteristics corresponding to a rotational angleθ in output signals produced by arithmetically operating output voltagesfrom the detecting coils with a reference voltage;

FIG. 11A is a schematic front view showing a principal part of arotary-type position detector device in accordance with anotherembodiment of the present invention;

FIG. 11B is a schematic sectional side view of the principal part of therotary-type position detector device;

FIG. 12A is a schematic front view showing a principal part of arotary-type position detector device in accordance with still anotherembodiment of the present invention;

FIG. 12B is a schematic sectional side view of the principal part of therotary-type position detector device;

FIG. 13 is a schematic front view showing a principal part of arotary-type position detector device in accordance with still anotherembodiment of the present invention;

FIGS. 14A-14C show an embodiment of the rotary-type position detectordevice in accordance with the present invention where only one detectingcoil is employed, of which FIG. 14A is a schematic front view of aprincipal part of the position detector device showing an example of aphysical positional relationship between the detecting coil of a statorsection and a magnetic-responsive member of a rotor section in theposition detector device, FIG. 14B is a schematic sectional side view ofthe part of the position detector device, and FIG. 14C is a blockdiagram showing an example of electric circuitry associated with thedetecting coil of the stator section;

FIG. 15 is a graph explanatory of position detecting operation of theembodiment shown in FIGS. 14A to 14C;

FIGS. 16A-16C show another embodiment of the rotary-type positiondetector device in accordance with the present invention where noreference voltage is used, of which FIG. 16A is a schematic front viewof a principal part of the position detector device showing an exampleof a physical positional relationship between individual detecting coilsof a stator section and a magnetic-responsive member of a rotor sectionin the position detector device, FIG. 16B is a sectional side view ofthe part of the position detector device shown in FIG. 16A, and FIG. 16Cis a block diagram showing an example of electric and electroniccircuitry associated with the detecting coils of the stator section

FIGS. 17A to 17C show a position detector device in accordance withstill another embodiment of the present invention, of which FIG. 17A isa schematic perspective view of a principal part of the positiondetector device, FIG. 17B is a sectional side view of the part of theposition detector device taken along an axis of a coil section, and FIG.17C is a block diagram showing an example of electric circuitryassociated with the coil section;

FIG. 18 is a graph explanatory of position detecting operation of theposition detector device shown in FIGS. 17A to 17C;

FIG. 19 is an electric circuit diagram showing a modification of theposition detector device of FIGS. 17A to 17C in relation to the coilsection;

FIG. 20 is an electric circuit diagram showing another modification ofthe position detector device of FIGS. 17A to 17C in relation to the coilsection;

FIGS. 21A to 21C show still another modification of the positiondetector device of FIGS. 17A to 17C, of which FIG. 21A is an electriccircuit diagram pertaining to the coil section, FIG. 21B is a graphshowing exemplary outputs from individual coils of the coil section, andFIG. 21C is a diagram explanatory of an exemplary manner in which theoutputs from the individual coils are synthesized through arithmeticoperations;

FIGS. 22A to 22C show still another modification of the positiondetector device of FIGS. 17A to 17C, of which FIG. 22A is an electriccircuit diagram pertaining to the coil section, FIG. 22B is a graphshowing exemplary outputs from individual coils of the coil section, andFIG. 22C is a diagram explanatory of an exemplary manner in which aposition is detected on the basis of the outputs from the individualcoils;

FIGS. 23A to 23E show still another modification of the positiondetector device of FIGS. 17A to 17C, of which FIG. 23A is an electriccircuit diagram pertaining to the coil section, FIG. 23B is a graphshowing exemplary outputs from individual coils of the coil section,FIG. 23C is a diagram explanatory of an exemplary manner in which theoutputs from the individual coils are synthesized through arithmeticoperations, FIG. 23D is a diagram explanatory of an exemplary manner inwhich a position is detected on the basis of the outputs from theindividual coils, and FIG. 23E is an electric circuit diagram showingmodified connection between the coils;

FIG. 24 is a schematic diagram showing a modified placement of the coilsin each of the embodiments shown in FIGS. 17A to 23E;

FIG. 25A is a schematic sectional view showing a modified positionalrelationship between a magnetism-responsive member and the coils in eachof the embodiments shown in FIGS. 17A to 23E;

FIG. 25B is a schematic sectional view showing another modifiedpositional relationship between the magnetism-responsive member and thecoils;

FIG. 26 is a schematic sectional view showing still another modifiedplacement of the coils in each of the embodiments shown in FIGS. 17A to23E;

FIG. 27 is a schematic sectional view showing still another modifiedplacement of the coils in each of the embodiments shown in FIGS. 17A to23E;

FIG. 28 is a side view schematically showing an example where theposition detector device in accordance with each of the embodiments ofFIGS. 17A to 27 is applied to detection of a position of an objectmoving along an arcuate or curved path;

FIG. 29 is a plan view showing an example of a hybrid-typemagnetism-responsive member comprising a combination of a magneticsubstance and an electrically conductive substance which is applicableto each of the embodiments of the present invention;

FIG. 30 is a perspective view showing an example of themagnetism-responsive member comprising a permanent magnet which isapplicable to each of the embodiments of the present invention;

FIGS. 31A and 31B are sectional views showing modifications of the coilplacement in the coil section shown in FIG. 25B;

FIG. 32 is a schematic axial sectional view showing still anotherembodiment of the position detector device of the present invention;

FIGS. 33A to 33C are diagram explanatory of principles on which theposition detector device of FIG. 32 detects a position, of which FIG.33A is a schematic perspective view of a principal part of the detectordevice showing a relationship between the coil section and themagnetism-responsive member of FIG. 32, FIG. 33B is a schematicsectional view taken along the axis of the coil section, and FIG. 33C isa block diagram showing electric circuitry associated with the coilsection;

FIG. 34 is a diagram explanatory of position detecting operation of theembodiment shown in FIGS. 33A to 33C, where part (A) is a graph showingexemplary outputs from individual coils and part (B) is a diagramexplanatory of an exemplary manner in which the outputs from theindividual coils are synthesized through arithmetic operations;

FIG. 35 is a diagram schematically showing another example of coildisplacement in the present invention;

FIG. 36 is a partly-sectional schematic view of a position detectordevice in accordance with still another embodiment of the presentinvention;

FIG. 37 is an electric circuit diagram of a coil section in the positiondetector device of FIG. 36;

FIGS. 38A to 38C are schematic views of a position detector device inaccordance with still another embodiment of the present invention, ofwhich FIG. 38A is a schematic perspective view of a principal part ofthe position detector device, FIG. 38B is a partly-sectional side viewthereof, and FIG. 38C is a view showing, in an unfolded condition, anexample of a pattern of a magnetism-responsive member formed on asurface of a rod-shaped base member and an arrangement of coilscorresponding thereof;

FIGS. 39A to 39E are schematic views of a position detector device inaccordance with still another embodiment of the present invention, ofwhich FIG. 39A is a cross-sectional view showing a rod-shaped basemember and a coil section, FIG. 39B is a view showing the rod-shapedbase member and coil section in an unfolded condition, FIG. 39C is ablock diagram of electric circuitry associated with individual coils,and FIGS. 39D end 39E are diagrams explanatory of position detectingoperation of the embodiment; and

FIGS. 40A to 40D are schematic views of a position detector device inaccordance with still another embodiment of the present invention, ofwhich FIG. 40A is a diagram showing, in an unfolded condition, fourdifferent patterns that are formed on a base member by amagnetism-responsive member, FIGS. 40B and 40C are diagrams explanatoryof position detecting operation of the embodiment, and FIG. 40D is ablock diagram of electric circuitry associated with individual coils.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a sectional view of principal part of a position detectordevice in accordance with an embodiment of the present invention,showing an example of a physical positional relationship between a coilsection 50 and a magnetism-responsive member 60 in the position detectordevice, which is taken along the axis of the coil section 50. FIG. 1B isa schematic plan view of the coil section 50 and magnetism-responsivemember 60, and FIG. 1C is a diagram showing an example of electriccircuitry associated with the coil section 50. The position detectordevice of FIG. 1 is constructed to detect a linear position of an objectto be detected (object of detection), in which the coil section 50 isfixed in position and the magnetism-responsive member 60 is linearlymovable relative to the coil section 50 in response to displacement ofthe object to be detected. However, it should be obvious that themagnetism-responsive member 60 may be fixed in position and the coilsection 50 may be arranged to linearly move relative to themagnetism-responsive member 60 in response to displacement of the objectto be detected.

The coil section 50 includes a single coil L1 to be excited by apredetermined A.C. signal, and a magnetic core 51 is provided in thecoil L1. The magnetism-responsive member 60 has a flat surface opposedto an end of the magnetic core 51 with an air gap interposedtherebetween, and this flat surface of the magnetism-responsive member60 is movable in a direction of arrow “x” or in an opposite directionthereto in response to a variation in the position of the object to bedetected, to thereby cause a dimensional variation in the interposingair gap. Such a variation in the interposing air gap, in turn, causes avariation in an amount of magnetic flux passing through the magneticcore 51 and coil L1, so that a self-inductance of the coil L1 varies.The variation in the self-inductance of the coil L1 also involves animpedance variation of the coil L1, which can be measured as a voltagebetween two terminals (“between-terminal voltage”) of the coil L1. Forthe purpose of describing the principles of the present invention, let'sassume that the magnetism-responsive member 60 is made of a magneticsubstance such as iron. The position detector device thus constructed issuitable for use in detecting a minute or microscopic displacement of,for example, a film such as a diaphragm. If the diaphragm, which is theobject to be detected, is made of a magnetic (orelectrically-conductive) material, then the diaphragm itself can becaused to function as the magnetism-responsive member 60. In analternative, the magnetism-responsive member 60 in the form of a film orsurface may be pasted or coated on the diaphragm or the like to bedetected.

In FIG. 1A, a maximum movable range of the magnetism-responsive member60 is illustrated by points “a” and “b”. The “a” point represents aposition where the member 60 is located farthest from the coil L1, whilethe “b” point represents a position where the member 60 is locatedclosest to the coil L1. FIG. 2A is a graph illustrating a variationcurve of the impedance of the coil L1 (vertical axis z) relative to theposition of the object to be detected (horizontal axis x). The impedanceof the coil L1 when the magnetism-responsive member 60 is at the “a”point is denoted by “Za”, and the impedance of the coil L1 when themagnetism-responsive member 60 is at the “b” point is denoted by “Zb”.Further, the voltage between the terminals of the coil L1, i.e., outputvoltage from the coil L1, presents a minimum level (minimum amplitudecoefficient) when the coil L1 has the impedance Za, but presents amaximum level (maximum amplitude coefficient) when the coil L1 has theimpedance Zb.

As the relative position of the magnetism-responsive member 60 changesfrom the “a” point to the “b” point, the voltage between the terminals(i.e., between-terminal voltage) of the coil L1 varies progressivelyfrom a minimum value corresponding to the impedance Za to a maximumvalue corresponding to the impedance Zb. Thus, first and secondreference voltages Va and Vb are set, as appropriate, within a range ofvalues which the between-terminal voltage of the coil L1 may take.Namely, of the maximum movable range from the “a” point to the “b”point, an appropriate detection section R is selected. If an amplitudecoefficient level (i.e., impedance) of the between-terminal voltage ofthe coil L1 occurring in correspondence with the start point of thedetection section R is represented by “Pa”, the between-terminal voltageof the coil L1, i.e., output voltage Vx, from the coil L1, correspondingto the start point of the detection section R can be represented by “Pasin ωt”, which is set as the first reference voltage Va; namely,

Va=Pa sin ωt

Further, If an amplitude coefficient level (i.e., impedance) of thebetween-terminal voltage of the coil L1 occurring in correspondence withthe end point of the detection section R is represented by “Pb”, thebetween-terminal voltage of the coil L1, i.e., output voltage Vx, fromthe coil L1 corresponding to the end point of the detection section Rcan be represented by “Pb sin ωt”, which is set as the second referencevoltage Vb; namely,

Vb=Pb sin ωt

As shown in FIG. 1C, the detecting coil L1 is excited, at a constantvoltage or current, by a predetermined single-phase A.C. signal(provisionally denoted by “sin ωt”) generated by an A.C. power supply30. Because the inductance of the detecting coil L1 is variable inresponse to a changing position of the object to be detected as notedabove, it is illustrated in the figure equivalently as a variableinductance. There are provided other coils Lr1 and Lr2 as circuits forgenerating the first and second reference voltages Va and Vb, which arealso driven by the A.C. signal generated by the A.C. power supply 30.Once these elements are set in order to determine the desired detectionsection R, they are fixed at these settings for subsequent use.

Arithmetic operation circuit 31A subtracts the first reference voltageVa from the output voltage Vx from the detecting coil L1. If theamplitude coefficient of the output voltage Vx from the detecting coilL1 is represented by a function A(x), then the arithmetic operationcircuit 31A performs the following arithmetic operations similar toExpression (1) above:

Vx−Va=A(x)sin ωt−Pa sin ωt={A(x)−Pa}sin ωt

Because A(x) equals Pa at the start point of the detection section R,the amplitude coefficient “A(x)−Pa”, which is the result of thesearithmetic operations, becomes “0”. On the other hand, at the end pointof the detection section R, A(x) equals Pb, so that the amplitudecoefficient “A(x)−Pa”, which is the result of these arithmeticoperations, equals “Pb−Pa”. Thus, the “A(x)−Pa”, the result of thesearithmetic operations, presents a function characteristic increasingprogressively from “0” to “Pb−Pa”. If the maximum value “Pb−Pa” isregarded equivalently as “1”, then the amplitude coefficient “A(x)−Pa”of the A.C. signal based on the above expression varies from “0” to “1”within the detection section R, and the function characteristic of theamplitude coefficient, as shown in FIG. 2B, can be likened to acharacteristic of a first quadrant (i.e., a 0°-90° region) in the sinefunction. Therefore, the amplitude coefficient “A(x)−Pa” of the A.C.signal based on the above expression can be expressed equivalently usingsine (approximately, 0°≦θ≦90°). Although FIG. 2B shows only an amplitudecoefficient curve sin θ of the sine function characteristic relative toa position x, an actual output from the arithmetic operation circuit 31Ais an A.C. signal “sin θ sin ωt” having an amplitude level thatcorresponds to the amplitude coefficient sin θ.

Arithmetic operation circuit 31B computes a difference between theoutput voltage Vx from the detecting coil L1 and the second referencevoltage Vb and performs the following arithmetic operations similar toExpression (2) above:

Vb−Vx=Pb sin ωt−A(x)sin ωt={Pb−A(x)}sin ωt

Because A(x) equals Pa at the start point of the detection section R,the amplitude coefficient “Pb−A(x)”, which is the result of thesearithmetic operations, equals “Pb−Pa”. On the other hand, at the endpoint of the detection section R, A(x) equals Pb, so that the amplitudecoefficient “Pb−A(x)”, which is the result of these arithmeticoperations, becomes “0”. Thus, the “Pb−A(x)”, the result of thesearithmetic operations, presents a function characteristic decreasingprogressively from “Pb−Pa” to “0”. If the maximum value “Pb−Pa” isconsidered equivalently to be “1”, then the amplitude coefficient“Pb−A(x)” of the A.C. signal based on the above expression varies from“1” to “0” within the detection section R, and the functioncharacteristic of the amplitude coefficient, as shown in FIG. 2B, can belikened to a characteristic of a first quadrant (i.e., a 0°-90° region)in the cosine function. Therefore, the amplitude coefficient “Pb−A(x)”of the A.C. signal based on the above expression can be expressedequivalently using cos θ (approximately, 0°≦θ≦90°). Although FIG. 2Bshows only an amplitude coefficient curve cos θ of the cosine functioncharacteristic relative to the position x, an actual output from thearithmetic operation circuit 31A is an A.C. signal “cos θ sin ωt” havingan amplitude level that corresponds to the amplitude coefficient cos θ.The subtraction by the circuit 31B may be “Vx−Vb” rather than “Vb−Vx”.

In this way, there can be generated two A.C. output signals that presentrespective amplitude levels of sine and cosine function characteristics(sin θ sin ωt and cos θ sin ωt) in response to a current position x ofthe object to be detected. These A.C. output signals are similar in formto output signals from the conventional position detectors commonlyknown as “resolvers” and can be utilized effectively in variousapplications. For example, the two resolver-type A.C. output signalsgenerated by the arithmetic operation circuits 31A and 31B are sent to aphase detection circuit (or amplitude-to-phase converter) 32, which candetect the position of the object to be detected in absoluterepresentation by measuring phase values θ of the sine and cosinefunctions sin θ and cos θ, defining the amplitude values, from acorrelation between the amplitude values of the two A.C. output signals.The phase detection circuit 32 may be implemented such as by a techniquedisclosed by the inventors of the present invention in Japanese PatentLaid-open Publication No. HEI-9-126809 (corresponding to U.S. Pat. No.5,710,509). For example, an A.C. signal sin θ cos ωt is generated byelectrically shifting the first A.C. output signal sin θ sin ωt by 90°,two A.C. signals sin(ωt+θ) and sin(ωt−θ) phase-shifted in aphase-advancing or phase-delaying direction in accordance with θ (i.e.,signals having their phase component θ converted into A.C. phase shifts)are generated by additively and subtractively synthesizing this signalsin θ cos ωt and the second A.C. output signal cos θ sin ωt, in such amanner that data indicative of a detected stroke position (strokeposition detecting data) can be obtained by measuring the phase θ. Thisphase detection circuit 32 may be implemented either by a dedicatedcircuit in the form of an LSI or by software processing using a CPU,processor, computer or the like. In an alternative, aconventionally-known R-D converter normally used for processing aresolver output may be used in the phase detection circuit 32. Detectionof the phase component θ in the phase detection circuit 32 may beperformed by an analog process using an integration circuit and thelike, rather than by a digital process. Alternatively, digital detectingdata indicative of a rotational position θ may be generated by a digitalphase detection process and then analog detecting data indicative of therotational position e may be obtained by converting the digitaldetecting data into analog representation. Of course, the A.C. outputsignals sin θ sin ωt and cos θ sin ωt from the arithmetic operationcircuits 31A and 31B may be output directly without being processed bythe phase detection circuit 32, in which case the detection circuit 32may be omitted.

If there is a linear correspondence between the phase angle θ and theposition x of the object to be detected, the amplitudes in the A.C.output signals sin θ sin ωt and cos θ sin ωt of the sine and cosinefunction characteristics will not present real sine and cosine functioncharacteristics. However, the phase detection circuit 32 carries out thephase detection process on these A.C. output signals sin θ sin ωt andcos θ sin ωt as apparently having real sine and cosine functioncharacteristics. As a result of this phase detection process, thedetected phase angle θ will not present linearity with respect to theposition x of the object to be detected. In detecting the position,however, the non-linearity between the detection output data (detectedphase angle θ) and the actual position of the object to be detected doesnot matter very much. Namely, it is only necessary to be able to performthe position detection with predetermined repetitive reproducibility.Further, if necessary, the output data from the phase detection circuit32 may be converted into other data form by use of an appropriate dataconversion table so that accurate linearity can be readily providedbetween the detection output data and the actual position of the objectto be detected. Accordingly, the “amplitude characteristics of the sineand cosine functions” referred to in connection with the presentinvention need not necessarily present real sine and cosine functioncharacteristics; in effect, they may be something like those of atriangular waveform, as illustratively shown in FIG. 2B, as long as theypresent such tendencies. In other words, it is only necessary that thesine and cosine functions in the present invention be similar totrigonometric functions such as a sine function. In the illustratedexample of FIG. 2B, if the horizontal axis represents the phase angle θand has given non-linear calibrations, even a function, apparentlyappearing as a triangular waveform when the horizontal axis calibrationsare assumed to represent the positions x, can be said to be a sine orcosine function with respect to the phase angle θ.

The following paragraphs describe compensation of temperature driftcharacteristics. Even when the impedance of the detecting coil L1 variesin response to a change in temperature, the subtractive arithmeticoperations in the arithmetic operation circuits 31A and 31B can cancelout a temperature drift, provided that the first and second referencevoltages Va and Vb have temperature drift characteristics similar tothose of the detecting coil L1. For this purpose, it is preferable thatthe coils Lr1 and Lr2, similar in characteristics to the detecting coilL1, be used for generation of the reference voltages and placed in antemperature environment similar to that of the detecting coil L1 (i.e.,relatively close to the detecting coil L1). However, thereference-voltage-generating coils Lr1 and Lr2 need not necessarily besimilar in characteristics to the detecting coil L1 although preferable,and they may be constructed to have temperature drift characteristicssubstantially similar to those of the detecting coil L1, e.g., byadjustment of additional resistors or the like. Further, to constructthe reference-voltage generation circuits, resistors or other suitableconstant-voltage-generating circuit may be used in place of theabove-mentioned coils Lr1 and Lr2.

As previously mentioned, variably setting the levels of the referencevoltages Va and Vb, i.e., the impedances Pa and Pb, would result invariably setting the detectable position range, i.e., the detectionsection R, used in the embodiment. Because every position within thedetection section R can always be detected as a phase angle θ within arange of about 90° irrespective of the length of the detectable positionrange, i.e., the detection section R, the resolution of the positiondetection can be variably set by variably setting the levels of thereference voltages Va and Vb. This means that the position detection canbe made with a super-high resolution even where very minute ormicroscopic displacement of the object is to be detected. For example,in a situation where the phase detection circuit 32 has a capability ofusing a 12-bit binary counter to detect a phase angle within the full360° rotational range with a resolution of 2¹² (=4096), the detectingresolution of a phase angle within the 90° range is “1024”, whichpermits minute or microscopic position detection with a super-highresolution of about 5 micron if the detectable position range, i.e., thedetection section R, is set to a length of 5 millimeters.

FIG. 3 shows a modification of the position detector device of FIG. 1,in which a moving direction x of a magnetism-responsive member 61differs from that of FIG. 1 and the magnetic the coil section 50 may beconstructed in the same manner as in FIG. 1. Specifically, FIG. 3A is aschematic sectional view of a principal part of the modified positiondetector device, and FIG. 3B is a schematic plan view of the part.Electric circuitry of the coil section 50 may be the same as in FIG. 1Cand thus illustration of the electric circuitry is omitted here to avoidunnecessary duplication. In FIG. 3A, a maximum movable range of themagnetism-responsive member 61 is illustrated by points “a” and “b”. The“a” point represents a position where the member 61 does not cover anend of the coil L1 so that the coil L1 produces a minimum output level.The magnetism-responsive member 61 is linearly movable from the “a”point in the direction of arrow x transversely to the end of the coilL1. Once the magnetism-responsive member 61, moving in the x direction,arrives at the “b” point as denoted by a dot-and-dash line 61′, itcompletely covers the end of the coil L1 so that the coil L1 produces amaximum output level. Generally, the position detector device of FIG. 3operates similarly to the embodiment of FIG. 1 so as to detect aposition of the object to be detected.

FIG. 4 is a partly-sectional side view showing still anothermodification of the position detector device of FIG. 1. In thismodification, the detecting coil L1 of the coil section 50 includes nomagnetic core 51, and a rod-shaped magnetism-responsive member 62 ismovable relative to the coil section 50 in a direction of arrow x toenter an interior space defined by the coil L1 in response todisplacement of the object to be detected. In this case too, a maximummovable range of the magnetism-responsive member 62 is illustrated bypoints “a” and “b”; however, the maximum movable range in thismodification corresponds substantially to the length of the coil L1. Themodified position detector device of FIG. 4 also operates similarly tothe embodiment of FIG. 1 so as to detect a position of the object to bedetected.

FIG. 5 is a partly-sectional side view showing still anothermodification of the position detector device of FIG. 1. In thismodification, the detecting coil L1 of the coil section 50 includes amagnetic core 51, and a magnetism-responsive member 63 in the shape of acylindrical sleeve is movable relative to the coil section 50 in adirection of arrow x to cause the coil L1 to enter an interior spacedefined by the member 63 in response to displacement of the object to bedetected. In this case too, a maximum movable range of themagnetism-responsive member 63 is illustrated by points “a” and “b”, andthe maximum movable range in this modification corresponds substantiallyto the length of the coil L1. However, the magnetism-responsive member63 of FIG. 5 is made of a non-magnetic substance of good electricalconductivity, such as copper, so that as the magnetism-responsive member63 moves closer to the coil L1 (the coil L1 enters deeper into theinterior space of the magnetism-responsive member 63), there occurs agreater eddy-current loss that causes the self-inductance of the coil L1to decrease. Therefore, the positions of the “a” and “b” points in thisfigure are reversed from those in the example of FIG. 4. The modifiedposition detector device of FIG. 5 also operates similarly to theembodiment of FIG. 1 so as to detect a position of the object to bedetected.

Further, FIG. 6 is a partly-sectional side view showing still anothermodification of the position detector device of FIG. 1. In thismodification, the detecting coil L1 of the coil section 50 includes amagnetic core 51, and a magnetism-responsive member 64 in the form of apermanent magnet shaped into a cylindrical sleeve is movable relative tothe coil section 50 in a direction of arrow x to cause the coil L1 toenter an interior space defined by the member 64 in response todisplacement of the object to be detected. When the permanent magnet 64gets sufficiently close the coil L1, a portion of the magnetic core 51near the coil is magnetically saturated or supersaturated, so that thebetween-terminal voltage of the coil L1 drops. The permanent magnet 64has a length at least equal to the length of the coil L1 in such amanner that the between-terminal voltage decreases progressively duringa movement of the permanent magnet 64 from one end to the other of thecoil L1. Namely, even in the case where a permanent magnet is used asthe magnetism-responsive member 64, a progressively decreasing variationcan be caused in the between-terminal voltage of the coil L1 during amovement of the permanent magnet 64 from one end to the other of thecoil L1. The permanent magnet 64 may have any other shape than a ring asillustrated, such as a rod, in which case the magnetism-responsivemember 64 comprising the permanent magnet may be arranged to pass theneighborhood of the coil L1 parallel to the axis of the coil L1. It ispreferable that the magnetic core 51 of the coil L1 in this modificationbe formed into a relatively thin shape so that magnetic saturation takesplace easily.

FIG. 7 shows still another embodiment of the position detector device ofthe present invention, in which the coil section 50 includes two coilsL1 and L2 and only one reference voltage Va is used. More specifically,FIG. 7A is a sectional view schematically showing an example of aphysical positional relationship between the coil section 50 and themagnetism-responsive member 60 in the position detector device, and FIG.7B is a diagram showing an example of electric circuitry associated withthe coil section 50. In the coil section 50 of FIG. 7, a magnetic core51 is inserted in one of the coils L1 as in the example of FIG. 1, andsimilarly, another magnetic core 51 is inserted in the other coil L2.These two coils L1 an d L2 are provided coaxially in opposed relation sothat ends of their respective magnetic cores 51 and 52 are opposed toeach other, and the magnetism-responsive member 60 in the shape of aflat plate is interposed between the coils L1 and L2.

As in the forgoing cases, a maximum movable range of themagnetism-responsive member 60 is illustrated by points “a” and “b”, andthe “a” point represents a position where the member 60 is locatedfarthest from the coil L1, while the “b” point represents a positionwhere the member 60 is located closest to the coil L1. Conversely, forthe other coil L2, the “a” point represents a position where the member60 is located closest to the coil L2, while the “b” point represents aposition where the member 60 is located farthest from the coil L2.Therefore, positions of the coils L1 and L2 relative to themagnetism-responsive member 60 change with opposite characteristics inresponse to displacement of the object to be detected, in response towhich the impedance of the coils L1 and L2 also varies with oppositecharacteristics. FIG. 8A is a graph illustrating variation curves of theimpedance of the coils L1 and L2 (vertical axis z) relative to theposition of the object to be detected (horizontal axis x). If theimpedance of the coil L1 when the magnetism-responsive member 60 is atthe “a” point is denoted by “Za” and the impedance of the coil L1 whenthe magnetism-responsive member 60 is at the “b” point is denoted by“Zb”, the impedance of the other coil L2 when the magnetism-responsivemember 60 is at the “a” point becomes “Zb” and the impedance of theother coil L2 when the magnetism-responsive member 60 is at the “b”point becomes “Zb”, due to the opposite characteristics.

As the relative position of the magnetism-responsive member 60 changesfrom the “a” point to the “b” point, the voltage between the terminals(i.e., between-terminal voltage) of the coil L1 varies progressivelyfrom a minimum value corresponding to the impedance Za to a maximumvalue corresponding to the impedance Zb. On the other hand, as therelative position of the magnetism-responsive member 60 changes from the“a” point to the “b” point, the between-terminal voltage of the othercoil L2 varies progressively from a maximum value corresponding to theimpedance Zb to a minimum value corresponding to the impedance Za. Inthis case, a single reference voltage Va is established incorrespondence with an amplitude coefficient level (i.e., impedance) Paof the between-terminal voltage of the coil L1 occurring incorrespondence with the start point of a suitable detection section Rselected out of the maximum movable range from the “a” point to the “b”point. Namely, the reference voltage Va is set in the same manner asnoted above, namely, as follows

Va=Pa sin ωt

As shown in FIG. 7B, the detecting coils L1 and L2 are excited, at aconstant voltage or current, by a predetermined single-phase A.C. signal(provisionally denoted by “sin ωt”) generated by an A.C. power supply30. Because the inductance of the detecting coils L1 and L2 is variablein response to a position of the object to be detected as noted above,it is illustrated in the figure equivalently as a variable inductance.There are provided another coils Lr1 as a circuit for generating thereference voltage Va, which is also driven by the A.C. signal generatedby the A.C. power supply 30.

Arithmetic operation circuit 31C subtracts the reference voltage Va fromthe output voltage Vx from the detecting coil L1, similarly to thearithmetic operation circuit 31A of FIG. 1. Namely, the arithmeticoperation circuit 31C performs the following arithmetic operationssimilar to Expression (1) above:

Vx−Va=A(x)sin ωt−Pa sin ωt={A(x)−Pa}sin ωt

Thus, as in the above-described case, the function characteristic of theamplitude coefficient in the A.C. output signal from the arithmeticoperation circuit 31C, as shown in FIG. 8B, can be likened to acharacteristic of a first quadrant (i.e., a 0°-90° range) in the sinefunction.

Arithmetic operation circuit 31D computes a difference between theoutput voltage Vy from the other detecting coil L2 and the referencevoltage Va and performs the following arithmetic operations similar toExpression (3) above:

 Vy−Va=A(y)sin ωt−Pa sin ωt={A(y)−Pa}sin ωt

As seen from FIG. 8A, the voltage between terminals (between-terminalvoltage) Vy of the coil L2 presents a progressively-decreasing variationcurve of a characteristic opposite to that of the between-terminalvoltage Vx of the coil L1, and the output voltage Vy produced from thecoil L2 in correspondence with the start point of the detection sectionR is provisionally represented by Pa′ sin ωt that is representative of amaximum value. Because A(y) equals Pa′ at the start point of thedetection section R, the amplitude coefficient “A(y)−Pa” of the A.C.output signal from the arithmetic operation circuit 31D equals “Pa′−Pa”representing “maximum value−minimum value”, which therefore becomes amaximum value that can be regarded equivalently as “1”. At the end pointof the detection section R, on the other hand, A(y) equals Pa, so thatthe amplitude coefficient “A(y)−Pa” of the A.C. output signal based onthe above arithmetic operations becomes “0”. Thus, the amplitudecoefficient “A(y)−Pa” of the A.C. output signal from the arithmeticoperation circuit 31D presents a function characteristic progressivelydecreasing from the “Pa′−Pa” (namely, “1”) to “0” within the range ofthe detection section R. This function characteristic of the amplitudecoefficient can be likened to a characteristic of a first quadrant(i.e., a 0°-90° range) in the cosine function. Therefore, the amplitudecoefficient “A(y)−Pa” of the A.C. output signal from the arithmeticoperation circuit 31D can be expressed equivalently using cos θ(approximately, 0°≦θ≦90°) as shown in FIG. 8B.

Thus, also in the case where two detecting coils L1 and L2 and a singlereference voltage Va are used, there can be generated two A.C. outputsignals that present respective amplitude levels of sine and cosinefunction characteristics (sin θ sin ωt and cos θ sin ωt) in response toa current position of the object to be detected. Further, in this casetoo, the sine and cosine functions present characteristics within therange of about one quadrant (90°), so that any position within thedetectable position range, i.e., the detection section R, can bedetected as a phase angle θ within the range of about 90°. In addition,the detectable position range, i.e., the detection section R, can bevariably set by variably setting the level of the reference voltage Va,which allows the detecting resolution to be adjusted. Furthermore,similarly to the embodiment of FIG. 1, the modified embodiment of FIG. 7permits effective compensation of temperature drift characteristics.

It is also important to note that the modifications of FIGS. 3 to 6applicable to the embodiment of FIG. 1 are also applicable to theembodiment of FIG. 7 in the same manner as described above. Details ofhow to modify the embodiment of FIG. 7 should be obvious from FIGS. 3 to6 and are not specifically illustrated to avoid unnecessary duplication.

Note that in each of the above-described embodiments, themagnetism-responsive member 60, 61 or 62 may be made of a non-magneticsubstance of good electrical conductivity, such as copper. In such acase, the inductance of each of the detecting coils decreases due to aneddy-current loss, and the between-terminal voltage decreases as themagnetism-responsive member 60, 61 or 62 moves closer to the coil. Inthis case too, the position detecting operations can be performed in themanner as described above. Also note that the magnetism-responsivemember may be of a hybrid type comprising a combination of a magneticsubstance and an electrically conductive substance.

Further, although the A.C. output signals are provided in sine andcosine phases (i.e., as resolver-type output signals), the presentinvention is not so limited; for example, the A.C. output signals may beprovided in three phases (the amplitude functions of the individualphases may be, for example, sin θ, sin(θ+120) and sin(θ+240)).

Now, a description will be made about several examples of rotational orrotary-type position detector devices as other preferred embodiments ofthe present invention.

FIGS. 9A-9C show an embodiment of a rotary-type position detector devicearranged in such a way that amplitude variations throughout a fullelectric angle range of 0° to 360° can be obtained in two A.C. outputsignals having amplitudes that present sine and cosine functioncharacteristics. More specifically, FIG. 9A is a schematic front view ofa principal part of the rotary-type position detector device, whichshows an example of a physical positional relationship between detectingcoils 41, 42 of a stator section 40 and a magnetic-responsive member 21of a rotor section 20 in the position detector device. FIG. 9B is asectional side view of the part of the rotary-type position detectordevice shown in FIG. 9A, and FIG. 9C is a block diagram showing anexample of electric and electronic circuitry associated with thedetecting coils 41 and 42. The magnetic-responsive member 21 of apredetermined shape, such as an eccentric disk shape, is mounted on arotation shaft 22 which is an object to be detected here, to therebyconstitute the rotor section 20. The following description is made inrelation to a case where the magnetic-responsive member 21 is made of amagnetic substance such as iron. The stator section 40 is opposed to therotor section 20 in a thrust direction of the rotation shaft 22.

The stator section 40 includes the two coils 41 and 42 as detectingcoils, which are disposed on a stator base 44 and spaced apart from eachother at a predetermined interval in a circumferential direction of themagnetic-responsive member 21. The predetermined interval in thecircumferential direction is such an interval that forms an angle of 90°relative to the rotation shaft 22. The detecting coils 41 and 42 arewound on iron cores (magnetic cores) 45 and 46, respectively, and amagnetic flux passing through the coils 41 and 42 is oriented in theaxial direction of the rotation shaft 22. Air gap is formed between endsurfaces of the coil iron cores 45 and 46 of the coils 41 and 42 and asurface of the magnetic-responsive member 21 of the rotor section 20, sothat the rotor section 20 rotates relative to the stator section 40 in anon-contact fashion. The relative positions between the rotor section 20and the stator section 40 are established via a not-shown mechanism insuch a manner that the distance between the rotor section 20 and thestator section 40 defined by the air gap is kept constant. Due to thepredetermined shape, such as an eccentric disk shape, of themagnetic-responsive member 21 of the rotor section 20, the areas of theend surfaces of the coil iron cores 45 and 46 that are opposed to themagnetic-responsive member 21 with the air gap interposed therebetweenwill vary in accordance with a varying rotational position of themagnetic-responsive member 21. Such variations in the areas of the endsurfaces of the coil iron cores 45 and 46 opposed to themagnetic-responsive member 21 vary the amount of the magnetic fluxpassing through the iron cores 45 and 46 and then through the coils 41and 42, which results in variations in the self-inductance of the coils41 and 42 and hence variations in the impedance of the coils 41 and 42.

The predetermined shape of the magnetic-responsive member 21 of therotor section 20 in this embodiment is chosen such that an ideal sinefunction curve can be provided. For example, in order to provide onecycle of a sine function curve per rotation of the rotation shaft 22,the magnetic-responsive member 21 may generally be formed into asubstantially eccentric disk shape as mentioned above; preciselyspeaking, however, it is known that the magnetic-responsive member 21can be formed into an appropriately distorted shape or a heart-likeshape depending on various design specifications such as the shapes ofthe coils and iron cores. Because choosing the shape of themagnetic-responsive member 21 and hence the rotor 20 is not an essentialpart of the present invention and the rotor may have any one of theshapes employed in known or unknown variable-reluctance-type rotationdetectors, no further reference will be made to the rotor shape. Whatthe predetermined shape of the magnetic-responsive member 21 of therotor section 20 is like is not important here; briefly speaking, it isonly necessary that variations in the inductance, i.e., impedance, ofthe coils 41 and 42 responding to a varying rotational position of therotor section 20 be designed as appropriately as possible to be similarto the ideal sine function curve.

FIG. 10A is a graph showing, by A(θ), an ideal sine function curve ofthe impedance of one of the coils 41 responding to a variation in arotational angle θ and also showing, by B(θ), an ideal sine functioncurve of the impedance of the other coil 42 responding to the variationin the rotational angle θ. As apparent, because the other coil 42 isshifted from the coil 41 by 90°, the curve B(θ) represents a cosinefunction. Thus, if a center point of increasing and decreasingvariations (upward and downward swings) in each of the curves A(θ) andB(θ) is represented by Po and an amplitude of the swing is representedby P,

A(θ)=Po+P sin θ

B(θ)=Po+P cos θ

Note that no significant inconvenience will arise in description of thepresent invention even if the amplitude P is regarded as “1” andignored, the amplitude P is not considered in the following description.

As shown in FIG. 9C, the detecting coils 41 and 42 are excited, at aconstant voltage or current, by a predetermined single-phase,high-frequency A.C. signal (provisionally denoted by “sin ωt”) generatedby an A.C. power supply 30. If between-terminal voltages of the coils 41and 42 are represented by “Vs” and “Vc”, respectively, they can beexpressed by the following expressions with the rotational angle θ to bedetected used as a variable:

Vs=A(θ)sin ωt=(Po+sin θ)sin ωt

Vc=B(θ)sin ωt=(Po+cos θ)sin ωt

Coil (dummy coil) 43 functions to generate a reference voltage Vr and ithas a predetermined impedance corresponding to, for example, the centerpoint Po. This coil 43 is mounted on the stator base 44, as shown inFIGS. 9A and 9B, at such a position where it always remains unaffectedby a movement of the magnetic-responsive member 21 of the rotor section20 and is placed under same temperature drift conditions as thedetecting coils 41 and 42. This arrangement serves the purpose ofcompensating for temperature drifts of the detecting coils 41 and 42.This coil (dummy coil) 43 is also excited by the A.C. signal, and itsbetween-terminal voltage, i.e., the reference voltage Vr, can beexpressed as

Vr=Po sin ωt

Note that if the dummy coil 43 is masked with a magnetic material toprovide a magnetic shield against the influence of themagnetic-responsive member 21, then the dummy coil 43 may be positionednear the magnetic-responsive member 21.

The output voltages Vs, Vc and Vr from the above-mentioned coils 41, 42and 43 are given to an analog arithmetic operation circuit 31 forarithmetic operations based on the following mathematic expressions.Thus, there are generated, from the analog arithmetic operation circuit31, two A.C. output signals of respective amplitudes that present sineand cosine function characteristics (i.e., two A.C. output signalshaving amplitude function characteristics phase-shifted from each otherby 90°) corresponding to a current position θ of the object to bedetected. Namely, the analog arithmetic operation circuit 31 subtractsthe reference voltage Vr from the output voltages Vs and Vc from thedetecting coils 41 and 42 as follows:

Vs−Vr=(Po+sin θ)sin ωt−Po sin ωt=sin θ sin ωt

Vc−Vr=(Po+cos θ)sin ωt−Po sin ωt=cos θ sin ωt

By performing arithmetic operations on the between-terminal voltages Vsand Vc of the detecting coils 41 and 42 and the reference voltage Vr inthe above-mentioned manner, there can be generated two A.C. outputsignals (sin θ sin ωt and cos θ sin ωt) having, as amplitudecoefficients, two cyclic amplitude functions (sin θ and cos θ) swingingin the positive and negative directions about the variation center pointwith an offset corresponding to the reference voltage Vr beingeliminated. FIG. 10B schematically shows these conditions only for the ecomponent (with no component of time t shown). In this way, theprovision of the two detecting coils 41 and 42 alone can give thesine-phase output signal sin θ sin ωt and cosine-phase output signal cosθ sin ωt similar to the outputs from the conventionally-known resolvers.

Rotational position θ of the object to be detected can be detected in anabsolute value by a phase detection circuit (or amplitude-to-phaseconverter) 32 measuring the phase component θ of the amplitude functionssin θ and cos θ in the A.C. output signals sin θ sin ωt and cos θ sin ωtof the sine and cosine function characteristics produced from the analogarithmetic operation circuit 31. The phase detection circuit 32 usedhere may be the same as the above-mentioned. Note that the signals sin θsin ωt and cos θ sin ωt from the analog arithmetic operation circuit 31may be output directly without being processed by the phase detectioncircuit 32, such as in a situation where three-phase signals, similar tothose provided by a conventionally-known “synchro”, have been producedby the analog arithmetic operation circuit 31. Also note that a block 33provided on the reverse side of the stator base 14 shown in FIG. 9Bindicates that necessary circuitry may be mounted on this portion. Forexample, only the arithmetic operation circuit 31, or all the circuitsof FIG. 9C including not only the arithmetic operation circuit 31 butalso the A.C. power supply 30 and phase detection circuit 32 may bemounted on the block 33. If the A.C. power supply 30 and phase detectioncircuit 32 are implemented by digital circuits, these circuits can beincorporated into an LSI chip of a much smaller size so that thecircuits can be attached together to the reverse side of the stator base44 as an integral or one-piece unit.

Now explaining compensation of temperature drift characteristics, theimpedance of the individual coils 41, 42 and 43 varies in response to atemperature change, so that their respective output voltages Vs, Vc andVr also vary. For example, each of the output voltages increases ordecreases in one direction, as shown in FIG. 10A by a dotted line incontradistinction to a solid-line curve. However, because theabove-mentioned arithmetic operations of “Vs−Vr” and “Vc−Vr” havecompletely compensated for temperature drifts in the A.C. output signalssin θ sin ωt and cos θ sin ωt of the sine and cosine functioncharacteristics which are the results of arithmetically synthesizing thecoil output voltages Vs, Vc and Vr, the output voltages have nosignificant influence of the temperature drifts. Therefore, in theapplication where the dummy coil 13 is employed as a circuit forgenerating the reference voltage Vr, the reference voltage Vr would alsovary in value in response to a change in ambient temperature (i.e.,drift with temperature), so that the subtractive arithmetic operationscan automatically compensate for the temperature drifts, therebyproviding for high-accuracy position detection. It should be obviousthat the circuit for generating the reference voltage Vr may beimplemented by any other suitable circuit than the coil, such as acombination of a coil and resistor or a resistor alone. For example,maximum and minimum values of the above-mentioned curves A(θ) and B(θ)may be detected, prior to the position detecting operations, to obtainan average value thereof, then evaluate a voltage level corresponding tothe center point Po of the increasing and decreasing variations in thevalues of the curves A(θ) and B(θ) and generate the evaluated voltage asthe reference voltage Vr.

Whereas, in the embodiment of FIGS. 9A and 9B, the ends of the ironcores (magnetic cores) 45 and 46 in the detecting coils 41 and 42 areshown and described as oriented in the thrust direction of the rotationshaft 22, the present invention is not so limited; of course, the endsof the iron cores 45 and 46 may be oriented in the radial direction ofthe rotation shaft 22. FIGS. 11A and 11B are a schematic front view anda sectional view, respectively, showing an example where the iron cores(magnetic cores) 45 and 46 in the detecting coils 41 and 42 are orientedin the radial direction of the rotation shaft 22. In these FIGS. 11A and11B, the same reference characters as in FIGS. 9A and 9B representelements of the same functions as in FIGS. 9A and 9B and thus will notbe described here to avoid unnecessary duplication. In FIGS. 11A and11B, the ends of the iron cores 45 and 46 in the detecting coils 41 and42 are oriented inwardly in the radial direction of the rotation shaft22 and are each opposed to the outer surface of the magnetism-responsivemember 21 of the rotor section 20 with an air gap interposedtherebetween. Due to the predetermined shape, such as an eccentric diskshape, heart-like shape or other appropriately designed shape, of themagnetic-responsive member 21 of the rotor section 20, a radial distancebetween each of the ends of the coil iron cores 41 and 42 and the outersurface of the magnetism-responsive member 21, which is defined by theinterposing air gap, is caused to vary in response to rotation of themagnetic-responsive member 21. Such variations in the distance betweenthe ends of the coil iron cores 41 and 42 and the outer surface of themagnetism-responsive member 21 vary the amount of the magnetic fluxpassing through the iron cores 45 and 46 and then through the coils 41and 42, which results in variations in the self-inductance of the coils41 and 42 and hence variations in the impedance of the coils 41 and 42.Thus, the arrangement of FIGS. 11A and 11B operates similarly to thearrangement of FIGS. 9A and 9B so as to detect a rotational position ofthe object to be detected. However, in the example of FIGS. 11A and 11B,the outer surface of the magnetic-responsive member 21 of the rotorsection 20 has a slightly greater axial length, so that even when therotation shaft 22, which is the object to be detected, mechanicallyshakes more or less in the thrust direction, the increased axial lengthof the magnetic-responsive member 21 can prevent variations in theradial distance defined by the air gap between the ends of the coil ironcores 41 and 42 and the outer surface of the magnetism-responsive member21, thereby preventing a undesired reduction in the detection accuracyof the device. For this reason, the arrangement of providing the radialair gap as shown in FIGS. 11A and 11B advantageously allows detection ofa rotational position to be made without being influenced by mechanicalshakes in the thrust direction in the case where the present inventionis applied to an environment or machine in which the rotation shaft 22is apt to shape in the thrust direction. It will be obvious that amodification similar to the one of FIGS. 11A and 11B is also possible inother embodiments shown in and after FIGS. 12A and 12B.

In each of the embodiments of FIGS. 9A and 9B and FIGS. 11A and 11B, thedetecting coils 41 and 42 are positioned in a predetermined limitedangular range (somewhat greater range than 90°) within one fullrotation. Thus, the stator base 44 need not have a great size, such asshown in FIGS. 9A and 9B and FIGS. 11A and 11B, which corresponds to thefull rotation of the rotor section 20; the stator base 44 may be formedinto a size corresponding only to a limited range of, say, a halfrotation, as shown in FIGS. 12A and 12B. Thus sizing the stator base 44allows the detector device to be installed while properly avoiding anobstacle 49, even where there is such an obstacle 49 at a place as shownin FIGS. 12A and 12B. Such a limited or biased placement of the coils 41and 42 in the stator section 40 will prove very useful in a situationwhere the rotary-type position detector device of the present inventionis to be installed in a previously-installed machine. Namely, in thecase where an obstacle 49 is already present within the predeterminedrotating angle range of the rotation shaft 22 and it is impossible toinstall the stator section 40 of a great size corresponding to the fullrotating range of the rotation shaft 22, the above-mentioned statorsection 40, with the coils 41 and 42 positioned at limited places withina limited angular range where the obstacle 49 is not present, canprovide a good solution and thus is very useful. Of course, in each ofthe embodiments, the rotation shaft 22, i.e., the object to be detected,itself may be designed to be able to rotate continuously through morethan one full rotation or through only a limited angular range less thanone full rotation (namely, reciprocatively swing within the limitedangular range). Further, the inventive position detector device of thetype where the air gap is formed with respect to the radial direction ofthe rotation shaft 22 as shown in FIGS. 11A and 11B is particularlyuseful because it can be readily installed when applied to a situationwhere an obstacle must be properly avoided in the installation of thedevice and during operation of the device as shown in FIGS. 12A and 12B.

In the examples of FIGS. 9A to 12B, the phase component θ in theamplitude functions of the A.C. output signals sin θ sin ωt and cos θsin ωt, provided on the basis of the outputs from the coils 41 and 42,corresponds to a mechanical rotational angle θ of the rotation shaft 22on a one-to-one basis. However, the present invention is not so limited,and the phase component θ in the amplitude functions may be set tocorrespond to n or 1/n times of the mechanical rotational angle θ of therotation shaft 22. One example where the phase component θ in theamplitude functions is set to correspond to two times of the mechanicalrotational angle is shown in FIG. 13, which is a schematic front viewsimilar to FIG. 9A. Namely, in the example of FIG. 13, two coils 41 and42 are positioned, in spaced apart relation to each other, form an angleof about 45° with respect the rotation shaft 22, and amagnetism-responsive member 21A of the rotor section 20 is designed intoa specific shape, such as an oval or near-oval shape, that can bringabout progressively increasing/decreasing variations of a two-cycle sinefunction in the impedance of the coils 41 and 42 per mechanical rotationof the rotation shaft 22. With this arrangement, the phase component θin the amplitude functions of the A.C. output signals sin θ sin ωt andcos θ sin ωt, provided on the basis of the outputs from the coils 41 and42, will present a value twice as great as the mechanical rotationalangle θ′ of the rotation shaft 22; that is, θ=2θ′. Various othermodifications than the one of FIG. 13 are also possible according to thebasic principles of the present invention.

FIGS. 14A to 14C show a position detector device in accordance withanother embodiment of the present invention, where the stator section 40includes only one detecting coil 41 and signals equivalent to two A.C.output signals sin θ sin ωt and cos θ sin ωt are generated on the basisof the output from the only coil 41 and reference voltage Vr. Morespecifically, FIG. 14A is a schematic front view of a principal part ofthe position detector device, which shows an example of a physicalpositional relationship between the detecting coil 41 of the statorsection 40 and a magnetic-responsive member 21B of the rotor section 20in the position detector device. FIG. 14B is a sectional side view ofthe part of the rotary-type position detector device shown in FIG. 14A,and FIG. 14C is a block diagram showing an example of electric andelectronic circuitry associated with the detecting coil 41 of the statorsection 40. In this embodiment, the magnetic-responsive member 21B ofthe rotor section 20 is generally in the shape of a swirl cam, which isdesigned such that the phase component θ in the amplitude functions ofthe A.C. output signals presents a variation within a range of about 90°relative to a mechanical rotational angle range of the rotation shaft22. Due to the swirl-cam shape of the rotor section 20, the embodimentof FIGS. 14A to 14C is somewhat unsuitable for position detection overthe full rotating range of the rotation shaft 22, but it is quitesuitable for detection of a rotational position within a predeterminedlimited mechanical rotational angle range less than one completerotation, i.e., excepting a stepped portion of the swirl-cam shape ofthe magnetic-responsive member 21B.

In the embodiment of FIGS. 14A to 14C, a between-terminal voltage Vs′ ofthe coil 41 presents a characteristic increasing (or decreasing)linearly in one direction within a predetermined mechanical rotationalangle range less than one complete rotation of the rotation shaft 22, astypically illustrated in FIG. 15. Of the thus-varying between-terminalvoltage Vs′ of the coil 41, a value twice as great as a minimum ornear-minimum value Vm is set as a reference voltage Vr′ and produced bymeans of the dummy coil 43. As shown in FIG. 14C, the output voltagesfrom the coils 41 and 43 are fed to the arithmetic operation circuit 31.In turn, the arithmetic operation circuit 31 of FIG. 14C subtracts ahalf of the reference voltage Vr′ (namely, Vm) from the between-terminalvoltage Vs′ of the coil 41 to thereby generate a first A.C. outputsignal having an amplitude characteristic increasing virtually from thezero level as denoted by Ve in FIG. 15, and also subtracts thebetween-terminal voltage Vs′ of the coil 41 from the reference voltageVr′ (namely, 2Vm) to thereby generate a second A.C. output signal havingan amplitude characteristic decreasing virtually from the level Vm asdenoted by Vf in FIG. 15.

Ve=Vs′−(Vr′/2)

Vf=Vr′−Vs′

The amplitude function characteristics of these A.C. output signalswithin a range W shown in FIG. 15 can be associated equivalently with asingle quadrant (90° range) of sine and cosine functions. For instance,the first A.C. output signal can be associated with the sine functionand treated equivalently as sin θ sin ωt, and the second A.C. outputsignal can be associated with the cosine function and treatedequivalently as cos θ sin ωt. However, the range of the phase componentθ with respect to the predetermined mechanical rotational angle range Wof the rotation shaft 22 is 90°. Thus, the phase angle θ detected viathe phase detection circuit 32 of FIG. 14C will take a value in therange of 0° to 90°, which will indicate, in absolute representation, arotational position within the predetermined mechanical rotational anglerange W of the rotation shaft 22.

If the first and second A.C. output signals Va and Vb presentingsubstantially linear amplitude variation characteristics are associatedwith the sine and cosine functions sin θ sin ωt and cos θ sin ωt, thentheir respective amplitude characteristics sin θ and cos θ will presentslight non-linearity relative to the predetermined mechanical rotationalangle range W of the rotation shaft 22, namely, they will not presentreal sine and cosine function characteristics. However, the phasedetection circuit 32 of FIG. 14C performs its phase detection processwhile apparently treating the A.C. output signals Va and Vb as signalssin θ sin ωt and cos θ sin ωt having sine and cosine functionalamplitude characteristics. As a consequence, the detected phase angle θdoes not show linearity relative to the rotational angle of the rotationshaft 22 that is the object to be detected here. However, in detectionof the rotational position, non-linearity between detection output data(indicative of the detected phase angle θ) and actual position to bedetected does not matter so much in many cases; namely, it is onlynecessary that the position detection be performed with predeterminedrepetitive reproducibility. Further, if necessary, the output data fromthe phase detection circuit 32 may be converted using an appropriatedata conversion table so that accurate linearity can be readily producedbetween the detection output data and the actual position to bedetected. Therefore, the A.C. output signals sin θ sin ωt and cos θ sinωt having sine and cosine functional amplitude characteristics asreferred to in connection with the present invention need notnecessarily present real sine and cosine function characteristics andmay, in effect, have characteristics of a triangular waveform or thelike (having a linear slope). In short, it is only necessary for theA.C. output signals sin θ sin ωt and cos θ sin ωt to have suchtendencies. Note that in the example of FIGS. 14A to 14C, two referencevoltages Va and Vb may be used as in the example of FIGS. 1A to 1C.

FIGS. 16A-16C show a position detector device in accordance with anotherembodiment of the present invention where the reference-voltagegeneration circuit is omitted and replaced by coils pairs varying in adifferential manner. More specifically, FIG. 16A is a schematic frontview of a principal part of the position detector device, which shows anexample of a physical positional relationship between the individualdetecting coils of the stator section 40 and the magnetic-responsivemember 21 of the rotor section 20 in the position detector device. FIG.16B is a sectional side view of the part of the position detector deviceshown in FIG. 16A, and FIG. 16C is a block diagram showing an example ofelectric and electronic circuitry associated with the detecting coil 41of the stator section 40. In this embodiment, the coil 41A is wound onan iron core 45A at an angular position spaced 180° from the sine-outputcoil 41, and the coil 42A is wound on an iron core 46A at an angularposition spaced 180° from the cosine-output coil 42; not that noreference-voltage-generating coil 43 is provided here. Themagnetic-responsive member 21 of the rotor section 20 may be shaped in asimilar manner to the example shown in FIGS. 9A and 9B. With sucharrangements, the impedance of the individual coils in each coil pairvaries in a differential manner, so that increasing/decreasingvariations in the between-terminal voltages of the individual coilspresent differential characteristics. That is, if the impedancevariation, i.e., output amplitude variation, of the coil 41 in the pairof the sine-phase coils 41 and 41A presents a function characteristic of“Po+P sin θ” in response to a rotational angle θ of the rotation shaft22, then the impedance variation, i.e., output amplitude variation, ofthe other coil 41A in the pair presents a function characteristic of“Po−P sin θ” in response to the rotational angle θ of the rotation shaft22. Similarly, if the impedance variation, i.e., output amplitudevariation, of the coil 42 in the pair of the cosine-phase coils 42 and42A presents a function characteristic of “Po+P cos θ” in response to arotational angle θ of the rotation shaft 22, then the impedancevariation, i.e., output amplitude variation, of the other coil 42A inthe pair presents a function characteristic of “Po−P cos θ” in responseto the rotational angle θ of the rotation shaft 22. Here, the amplitudeP is regarded as “1” and ignored just for convenience of description, asin the above-described cases.

As shown in FIG. 16C, the coils 41, 41A, 42 and 42A are each excited bya predetermined A.C. signal, and the between-terminal voltages Vs, Vsa,Vc and Vca of these coils 41, 41A, 42 and 42A present respective levelscorresponding to the rotational angle θ of the rotation shaft 22 asfollows:

Vs=(Po+sin θ)sin ωt

Vsa=(Po−sin θ)sin ωt

 Vc=(Po+cos θ)sin ωt

Vca=(Po−cos θ)sin ωt

For each of the coil pairs, the arithmetic operation circuit 31 computesa difference in the between-terminal voltages of the coils and therebygenerates an A.C. output signal having a predetermined cyclic amplitudefunction as its amplitude coefficient in the following manner:

Vs−Vsa=(Po+sin θ)sin ωt−(Po−sin θ)sin ωt=2 sin θ sin ωt

Vc−Vca=(Po+cos θ)sin ωt−(Po−cos θ)sin ωt=2 cos θ sin ωt

Thus, there can be generated two A.C. output signals (sin θ sin ωt andcos θ sin ωt) having, as amplitude coefficients, two cyclic amplitudefunctions (sin θ and cos θ) corresponding to the rotational angle θ ofthe rotation shaft 22 that is the object to be detected, in a similarmanner to outputs from the conventional resolvers. As opposed to theconventional resolvers, the present invention requires only a primarycoil and can eliminate a need for a secondary coil to produce an inducedoutput, so that the present invention can significantly simplify thenecessary coil structure and hence can provide a rotary-type positiondetector device of a greatly simplified structure. Note that thecircuitry for producing the difference in the between-terminal voltagesof the coils in each of the coil pairs may be simplified bydifferentially connecting the coils 41 and 41A and differentiallyconnecting the coils 42 and 42A to provide the respective differences“Vs−Vsa” and “Vc−Vca” without using the specific arithmetic operationcircuit 31.

Note that in the case where the magnetism-responsive member 21 is madeof a substance of good electrical conductivity, such as copper, theinductance of each of the coils decreases due to an eddy-current loss,and the between-terminal voltage of the coil decreases as themagnetism-responsive member 21 moves closer to the coil. In this casetoo, the position detecting operations can be performed in the manner asdescribed above. Also note that the magnetism-responsive member 21 maybe of a hybrid type comprising a combination of a magnetic substance andan electrically conductive substance. Further, the magnetism-responsivemember 21 may comprise a permanent magnet as in the case noted above.

It should also be noted that in relation to the type of positiondetector device which is designed to detect a rotational position of anobject swinging within a limited rotating range less than one fullrotation, each of the above-described embodiments may be constructedsuch that the magnetism-responsive member 21 is fixed while thedetecting coils 41 and 42 are provided for movement relative to themagnetism-responsive member 21 in response to displacement of the objectto be detected.

Further, although the A.C. output signals are provided in two phases,sine and cosine phases (i.e., as resolver-type output signals) in eachof the above-described embodiments, the present invention is not solimited; for example, the A.C. output signals may be provided in threephases (the amplitude functions of the individual phases may be, forexample, sin θ, sin(θ+120) and sin(θ+240)).

Also note that for excitation of the coils by the A.C. signal, there maybe employed the conventionally-known two-phase excitation scheme thatseparately excites at least two coils by sin ωt and cos ωt,respectively. However, the single-phase excitation as described above inrelation to the embodiments is more advantageous in many respects, suchas structural simplification and temperature-drift compensatingcharacteristics.

Next, a description will be made about still another embodiment of thepresent invention which is designed to performed arithmetic operationson combinations of output voltages from a plurality of detecting coils.

FIGS. 17A to 17C show a position detector device in accordance with theother embodiment of the present invention which is designed such thatamplitude variations can be produced over a full electric angle range of0° to 360° in two A.C. output signals of amplitudes presenting sine andcosine function characteristics. More specifically, FIG. 17A is aschematic perspective view of a principal part of the position detectordevice, which shows an example of a physical positional relationshipbetween a coil section 10 and a magnetism-responsive member 11 in theposition detector device. FIG. 17B is a sectional side view of the partof the position detector device taken along the axis of the coil section10, and FIG. 17C is a block diagram showing an example of electriccircuitry associated with the coil section 10. In the position detectordevice shown in FIGS. 17A to 17C that is directed to detecting a linearposition of an object to be detected, the coil section 10 is fixed whilethe magnetism-responsive member 11 is arranged to move linearly relativeto the coil section 10 in response to displacement of the object to bedetected. Conversely, the magnetism-responsive member 11 may be fixedwhile the coil section 10 is arranged to move linearly relative to themagnetism-responsive member 11 in response to displacement of the objectto be detected. The coil section 10 includes a plurality of coilsegments (in the illustrated example, six coil segments Lα, LA, LB, LC,LD and Lβ) disposed in series along a direction in which the object tobe detected is displaced, and these coil segments of the coil section 10are excited by a predetermined single-phase A.C. signal. For convenienceof description, let it be assumed here that these coil segments Lα, LA,LB, LC, LD and Lβ are equal to each other in the number of coil turns,coil length, etc. The magnetism-responsive member 11 is formed of amagnetic substance, such as iron, into a shape of a rod or the like, andmovable into a space defined by the coil segments of the coil section10. For example, as the magnetism-responsive member 11 moves rightwardin FIG. 17A, the tip 11 a of the magnetism-responsive member 11 firstenters the leading or first coil segments Lα, then enters the other coilsegments LA, LB, LC and LD sequentially in the order mentioned, andfinally then enters the last or sixth coil segment Lβ. Two-dots-and-dashline 11′ in FIG. 17B depicts the magnetism-responsive member 11 havingcompletely entered as far as the last coil segment Lβ.

Axial range corresponding to the four intermediate coil segments LA, LB,LC and LD constitutes an effective detecting range of the positiondetector device. If the axial length of each one of the intermediatecoil segments LA, LB, LC and LD is represented by “K”, then an axiallength four time as great as the length K equals the effective detectingrange. The coil segments Lα and Lβ located immediately before and afterthe effective detecting range 4K are auxiliary coil segments that areprovided in order to more reliably achieve cosine functioncharacteristics; these auxiliary coil segments Lα and Lβ may bedispensed with or omitted in a situation where very high detectingaccuracy is not required.

As shown in FIG. 17C, the individual coil segments Lα, LA, LB, LC, LDand Lβ are excited, at a constant voltage or current, by a predeterminedsingle-phase A.C. signal (“sin ωt”) generated by an A.C. power supply30. Voltages between the respective opposite ends (between-terminalvoltages) of these coil segments Lα, LA, LB, LC, LD and Lβ are denotedhere by “Vα”, “VA”, “VB”, “VC”, “VD” and “Vβ”, respectively, and taps13-19 are provided to take out these voltages Vα, VA, VB, VC, VD and Vβ.As may be readily understood, the coil segments Lα, LA, LB, LC, LD andLβ need not necessarily be physically-separated coils, and they may beimplemented by just a single continuous coil divided into six coillengths or portions by the intermediate taps 13-19; that is, the coilportion between the taps 13 and 14 functions as the coil segment Lα, thecoil portion between the taps 14 and 15 functions as the coil segmentLA, the coil portion between the taps 15 and 16 functions as the coilsegment LB, the coil portion between the taps 16 and 17 functions as thecoil segment LC, the coil portion between the taps 17 and 18 functionsas the coil segment LD, and the coil portion between the taps 18 and 19functions as the coil segment Lβ. The output voltages Vα, VA, VB, VC, VDand Vβ from the individual coil segments are delivered, in predeterminedcombinations, to analog arithmetic operation circuits 311 and 312, inwhich they are subjected to an addition and/or subtraction based onpredetermined mathematical expressions. Thus, these analog arithmeticoperation circuits 311 and 312 produce two A.C. output signals ofamplitudes that present sine and cosine function characteristics (i.e.,two A.C. output signals having amplitude function characteristicsphase-shifted from each other by 90°) corresponding to a currentposition of the object to be detected. For illustration purposes, theoutput signal from the analog arithmetic operation circuit 311 isdenoted by sin θ sin ωt while the output signal from the other analogarithmetic operation circuit 312 is denoted by and cos θ sin ωt. Theanalog arithmetic operation circuits 311 and 312 comprise operationalamplifiers OP1, OP2 and resistor circuits RS1, RS2.

It should be obvious that the present invention is not limited to theforegoing arrangements and the coil segments Lα, LA, LB, LC, LD and Lβmay be implemented by separate coils connected in series; in such acase, the separate coils may be excited together by a predeterminedsingle-phase A.C. signal or may be excited parallel via separateexciting circuits in a same phase by a predetermined single-phase A.C.signal. However, the above-described embodiment where a singlecontinuous coil is divided into a plurality of coil segments and theoutput voltages from these divided coil segments are taken out byintermediate taps is most preferable because it can be simplest instructure. Also note that the coil segments Lα, LA-LD and Lβ willhereinafter be referred to simply as “coils”.

With the above-described arrangements, as the magnetism-responsivemember 11 moves closer to or further or deeper into any one of thecoils, the self-inductance, i.e., impedance, of the coil increases, andthus the voltage between the opposite ends of the coil increasesprogressively during displacement of the tip 11 a of themagnetism-responsive member 11 from one end to the other of that coil.Here, because the coils Lα, LA, LB, LC, LD and Lβ are arranged in seriesalong the displacement direction of the object to be detected,progressively increasing (progressive incremental) variations in therespective voltages Vα, VA, VB, VC, VD and Vβ of the coils Lα, LA, LB,LC, LD and Lβ will occur sequentially, as illustratively shown in part(A) of FIG. 18, as the magnetism-responsive member 11 moves relative tothe coils in response to the displacement of the object to be detected.In part (A) of FIG. 18, a slope in each of the curves, indicative of theoutput voltage from any one of the coils, represents a region where thetip 11 a of the magnetism-responsive member 11 is moving from one endtoward the other of the coil in question. Typically, theprogressively-increasing variation curve of the voltage between theopposite ends of the coil, which takes place during the movement of themagnetism-responsive member 11 from the coil's one end to the other, canbe likened to a functional value variation within a 90° range of thesine or cosine function. Thus, by appropriately combining the outputvoltages Vα, VA, VB, VC, VD and Vβ from the coils Lα, LA, LB, LC, LD andLβ and performing an addition and/or subtraction between thecombinations, it is possible to produce two A.C. output signals sin θsin ωt and cos θ sin ωt of amplitudes that present sine and cosinefunction characteristics corresponding to a current position of theobject to be detected.

More specifically, the analog arithmetic operation circuit 311 canprovide an A.C. output signal presenting an amplitude curve of the sinefunction characteristic as shown in part (B) of FIG. 18, by performingarithmetic operations on the output voltages VA, VB, VC and VD from thecoils LA, LB, LC and LD in accordance with Expression (4) below; theA.C. output signal can be represented equivalently by “sin θ sin ωt”.

(VA−VB)+(VD−VC)  Expression (4)

Further, the other analog arithmetic operation circuit 312 can providean A.C. output signal presenting an amplitude curve of the cosinefunction characteristic as shown in part (B) of FIG. 18, by performingarithmetic operations on the output voltages Vα, VA, VB, VC, VD and Vβfrom the coils Lα, LA, LB, LC, LD and Lβ in accordance with Expression(5) below. Although the amplitude curve of the cosine functioncharacteristic as shown in part (B) of FIG. 18 actually presents a minuscosine function characteristic, i.e., “−cos θ sin ωt”, the amplitudecurve corresponds to the cosine function characteristic since itpresents a 90° shift relative to the sine function characteristic.Therefore, this can be said to be an A.C. output signal of the cosinefunction characteristic, which can be represented equivalently by “cos θsin ωt”.

(VA−Vα)+(VB−VC)+(Vβ−VD)  Expression (5)

Note that the following mathematical expression may be used instead ofExpression (5) above:

(VA−Vα)+(VB−VC)−VD  Expression (5′)

The A.C. output signal “−cos θ sin ωt” of the minus cosine functioncharacteristic evaluated by Expression (5) may be electricallyphase-inverted by 180° to thereby actually generate a signal of “cos θsin ωt” for use as the A.C. output signal of the cosine functioncharacteristic. However, in a situation where the A.C. output signal ofthe cosine function characteristic is used by a phase detection circuit32 at a succeeding stage for a subtractive arithmetic operation in theform of “−cos θ sin ωt”, the A.C. output signal “−cos θ sin ωt” of theminus cosine function characteristic can of course be used just as itis. Also note that the A.C. output signal “cos θ sin ωt” of the actualcosine function characteristic can be generated by performing thefollowing mathematical expression instead of Expression (5):

(VA−Vα)+(VC−VB)+(VD−Vβ)  Expression (5″)

The phase angle θ in the sine and cosine functions, which are amplitudecomponents of the individual A.C. output signals, corresponds to acurrent position of the object to be detected, and the phase angle θwithin a 90° range corresponds to the length K of one of the coils.Thus, the effective detecting range of the 4K length corresponds tophase angles θ ranging from 0° to 360°. Therefore, every position withinthe effective detecting range of the 4K length can be detected in anabsolute value by detecting such a phase angle θ.

Now, an explanation is given below about compensation of the temperaturecharacteristics in the embodiment. The impedance of the individual coilsvaries with a temperature change, and such an impedance variationresults in variations in the output voltages Vα, VA, VB, VC, VD and Vβ.For example, as illustrated in part (A) of FIG. 18, each of the outputvoltages would vary to increase or decrease in one direction as depictedby dotted line in contradistinction to a solid-line curve. However, inthe A.C. output signals sin θ sin ωt and cos θ sin ωt of the sine andcosine function characteristics, obtained by the additive andsubtractive syntheses of the output voltages, the variations wouldappear as positive and negative amplitude variations as shown by dottedlines in contradistinction with solid-line curves in part (B) of FIG.18. If an amplitude coefficient A is used, the A.C. output signals canbe represented as A sin θ sin ωt and A cos θ sin ωt, respectively, andit is this amplitude coefficient A that varies in response to a changein ambient temperature. As may be clear from this, the amplitudecoefficient A indicative of the temperature characteristics does notinfluence the phase angle θ in the sine and cosine functions. Thus, inthe present embodiment, temperature characteristics can be dulycompensated in an automatic fashion, to thereby achieve high-accuracyposition detection.

Every position of the object to be detected can be detected as anabsolute value by the phase detection circuit (or amplitude-to-phaseconverting means) 32 measuring the phase angle θ of the amplitudefunctions sin θ and cos θ in the A.C. output signals sin θ sin ωt andcos θ sin ωt of the sine and cosine functions. The phase detectioncircuit 32 may be designed in the same manner as noted above.

In this case too, if there is a linear correspondence between the phaseangle θ and the position x of the object to be detected, the amplitudesin the A.C. output signals sin θ sin ωt and cos θ sin ωt of the sine andcosine function characteristics will not present real sine and cosinefunction characteristics. However, the phase detection circuit 32carries out the phase detection process while regarding these A.C.output signals sin θ sin ωt and cos θ sin ωt as apparently having realsine and cosine function characteristics. As a result of this, thedetected phase angle θ will not present linearity with respect to theposition x of the object to be detected. In detecting a position,however, non-linearity between the detection output data (detected phaseangle θ) and the actual position of the object to be detected does notmatter very much and can be adjusted whenever necessary, as notedearlier.

Variation range of the phase angle θ of the amplitude functions sin θand cos θ in the A.C. output signals sin θ sin ωt and cos θ sin ωt ofthe sine and cosine functions may be set to be a limited angular rangenarrower than the full rotational range of 0° to 360° as employed in theabove-mentioned embodiment. In such a case, the structure of the coilscan be simplified to a significant degree. The detectable phase rangemay be set to be less than the full 360° range particularly where minuteor microscopic displacement of the object to be detected is to bedetected because the effective detecting range may be narrowed. Further,in various other cases, the detectable phase range may also be set to beless than the full 360° range, depending on a purpose of the positiondetection. Thus, the following paragraphs describe such modifications ofthe detectable phase range.

FIG. 19 is a block diagram showing an embodiment of the positiondetector device, in which phase variations can be produced over a rangeof 0° to 180°. In this position detector device of FIG. 19, the coilsection 10 includes two coils LA and LB corresponding to an effectivedetecting range of the device and two auxiliary coils Lα and Lβ locatedimmediately before and after the coils LA and LB. Analog arithmeticoperation circuit 313 receives respective between-terminal voltages Vα,VA, VB and Vβ output from the coils, so that the operation circuit 313performs an arithmetic operation as represented by Expression (6) belowto thereby generate an A.C. output signal sin θ sin ωt presenting anamplitude curve of a sine function characteristic and also performs anarithmetic operation as represented by Expression (7) below to therebygenerate an A.C. output signal cos θ sin ωt presenting an amplitudecurve of a cosine function characteristic.

VA−VB  Expression (6)

(VA−Vα)+(VB−Vβ)  Expression (7)

As may be readily understood with reference to a combined reference toFIGS. 19 and 18, the arithmetic operation represented by Expression (6)can generate an A.C. output signal sin θ sin ωt presenting an amplitudecurve of a sine function characteristic for the 0°-180° range, and thearithmetic operation represented by Expression (7) can generate an A.C.output signal cos θ sin ωt presenting an amplitude curve of a cosinefunction characteristic for a range of −90° to 270° (i.e., from minus90°, through 0°, plus 90° and 180°, to 270°. Similarly to theabove-described embodiments, the auxiliary coil Lβ can be omitted as inthe above-described cases. Every position within the effective detectingrange of the 2K length of the two coils LA and LB can be detected in anabsolute value by detecting the phase angle θ in the amplitudefunctions. It should be obvious that the mathematical expressionsemployed here may be modified as desired rather than being limited tothe above-mentioned alone. Namely, the mathematical expressions can bemodified by changing the angular range over which the 180°-wide phasevariation should arise. For example, in a situation where an effectivephase variation is to take place for an angular range of 180° to 360°, amathematical expression of “(Vα−VA)+(Vβ−VB)” may be used to generate anA.C. output signal sin θ sin ωt of a sine function characteristic, and amathematical expression of “(VB−VA)” may be used to generate an A.C.output signal cos θ sin ωt of a cosine function characteristic.

Further, FIG. 20 is a block diagram showing another embodiment of theposition detector device, in which phase variations can be produced overa range of 0° to 90°. In this position detector device of FIG. 20, thecoil section 10 includes a single coil LA corresponding to an effectivedetecting range of the device and two auxiliary coils Lα and Lβ locatedimmediately before and after the coil LA. Analog arithmetic operationcircuit 314 receives respective between-terminal voltages Vα, VA and Vβoutput from the coils, so that the operation circuit 314 performs anarithmetic operation as represented by Expression (8) below to therebygenerate an A.C. output signal sin θ sin ωt presenting an amplitudecurve of a sine function characteristic and also performs an arithmeticoperation as represented by Expression (9) below to thereby generate anA.C. output signal cos θ sin ωt presenting an amplitude curve of acosine function characteristic.

VA−Vβ  Expression (8)

VA−Vα  Expression (9)

As may be readily understood with reference to a combined reference toFIGS. 20 and 18, the arithmetic operation represented by Expression (8)can generate an A.C. output signal sin θ sin ωt presenting an amplitudecurve of a sine function characteristic for a range of 0°-180° (from 0°through 90° to 180°), and the arithmetic operation represented byExpression (9) can generate an A.C. output signal cos θ sin ωtpresenting an amplitude curve of a cosine function characteristic for arange of −90° to 90° (i.e., from minus 90°, through 0° to plus 90°.Therefore, the 0°-90° angular range can be allocated as the effectivedetecting range of the position detector device. In this case too, themathematical expressions employed may be modified as desired rather thanbeing limited to the above-mentioned. Namely, the mathematicalexpressions can be modified by changing the angular range over which the90°-wide phase variation should arise.

Whereas the embodiments have been described as including the auxiliarycoils Lα and Lβ located immediately before and after the effectivedetecting range, these auxiliary coils Lα and Lβ may be omitted. FIGS.21A to 21C shows such a modified embodiment which can produce phasevariations within a range of 0° to 180°. In this embodiment, the coilsection 10 includes two coils LA and LB corresponding to the effectivedetecting range of the position detector device. These coils LA and LBare disposed in series along the displacement direction of the object tobe detected, so that as the magnetism-responsive member 11 movesrelative to the coils LA and LB in response to displacement of theobject to be detected, the between-terminal voltages VA and VB of thecoils LA and LB vary to increase progressively in sequence asillustrated in FIG. 21B. Here, the voltage produced when themagnetism-responsive member 11 has not at all entered the coil isrepresented by “Vo” and the voltage produced when themagnetism-responsive member 11 has fully entered any one of the coils isrepresented by “VN”. If constant voltages Vo and VN are generated from asuitable constant voltage generator circuit and a sum (VN+Vo) of theconstant voltages Vo and VN is subtracted from a sum of thebetween-terminal voltages VA and VB, then the voltage obtained as thesubtracted result “VA+VB−VN−Vo” presents a cosine functioncharacteristic (or minus cosine function characteristic) over the0°-180° range as shown in FIG. 21C. On the other hand, a voltage (VA−VB)obtained by subtracting the voltage VB from the voltage VA presents asine function characteristic over the 0°-180° range as also shown inFIG. 21C.

Namely, by a subtracter circuit 315 performing a subtractive arithmeticoperation (“VA−VB”) between the between-terminal voltage VA of the coilLA and the between-terminal voltage VB of the coil LB in the example ofFIG. 21A, there can be generated an A.C. output signal sin θ sin ωtpresenting a sine function characteristic. Also, by an adder circuit 316adding together the between-terminal voltages VA and VB of the coils LAand LB and a subtracter circuit 317 performing an operation(“VA+VB−VN−Vo”) subtracting the sum of the constant voltages VN and Vo,generated by a constant voltage generator circuit 27, from the sum ofthe between-terminal voltages VA and VB, there can be generated an A.C.output signal cos θ sin ωt presenting a cosine function characteristic.Let it be assumed here that the constant voltages VN and Vo generated bythe constant voltage generator circuit 27 are caused to vary withtemperature characteristics similar to those of the coils LA and LB; forthat purpose, it is only necessary that the constant voltage generatorcircuit 27 be in the form of a dummy coil that has characteristics equalto those of the coil LA or LB and is excited by the same exciting A.C.signal. If a magnetic core similar in characteristics to themagnetism-responsive member 11 is always inserted in such a dummy coil,the same constant voltage as the maximum voltage produced VN producedwhen the magnetism-responsive member 11 has fully entered any one of thecoils can be obtained constantly with temperature characteristics. If nosuch magnetic core is inserted in the dummy coil, then the same constantvoltage as the minimum voltage value Vo can be obtained.

The above-mentioned constant voltage generator circuit 27 is applicablenot only to the case where the number of the coils is two but also toother cases where a smaller or greater number of the coils are employed.For example, in a situation where three coils LA, LB and LC are used tocause phase variations over a 0°-270° range, the A.C. output signal sinθ sin ωt presenting a sine function characteristic can be generatedthrough an arithmetic operation of “VA−VB−VC+Vo” using the outputvoltages VA, VB and VC and constant voltages VN and Vo from the constantvoltage generator circuit 27, and the A.C. output signal cos θ sin ωtpresenting a cosine function characteristic can be generated through anarithmetic operation of “VA+VB−VC−VN”.

As another example, only one coil may be provided in correspondence withthe effective detecting range of the position detector device. In thiscase, a phase variation width within the effective detecting rangecorresponding to the length K of the only coil is less than 90°. FIGS.22A to 22C show such an example, where, as shown in FIG. 22A, the onlycoil LA is connected in series with a resistor R1. With thisarrangement, as the amplitude component in the between-terminal voltageVA of the coil LA progressively increases, as shown in FIG. 22B, inresponse to a movement of the magnetism-responsive member 11, theamplitude component in the between-terminal voltage drop VR of theresistor Ri decreases progressively. If the between-terminal voltage VRof the resistor R1 is regarded as an A.C. output signal sin θ sin ωt ofa sine function characteristic and the between-terminal voltage VA ofthe coil LA is regarded as an A.C. output signal cosOsincot of a cosinefunction characteristic, they can be associated with characteristicswithin a given less-than-90° angular range where the sine and cosinefunctions cross each other. Therefore, by supplying these A.C. outputsignals to the phase detection circuit 32, a phase angle θ within theless-than-90° angular range in question can be detected in an absolutevalue.

FIGS. 23A to 23E show a modification of the embodiment shown in FIGS.22A to 22C, where a dummy coil LN is provided in place of the resistorRi. The dummy coil LN is connected in series with the detecting coil LAthat would be affected by the movement of the magnetism-responsivemember 11, but is not itself affected the movement of themagnetism-responsive member 11. By the provision of the dummy coil LN,the same constant voltage as the maximum voltage produced VN producedwhen the magnetism-responsive member 11 has fully entered any one thecoils can be obtained constantly with temperature characteristics. Thus,the between-terminal voltages VA and VN of the coil LA and dummy coil LNcorresponding to the movement of the magnetism-responsive member 11 areproduced in a manner as shown in FIG. 23B. Arithmetic operation circuit318 computes these voltages VA and VN in accordance with predeterminedmathematical expressions; for example, the arithmetic operation circuit318 generates an A.C. output signal sin θ sin ωt of a sine functioncharacteristic through an arithmetic operation of “VA+VN” and generatesan A.C. output signal cos θ sin ωt of a cosine function characteristicthrough an arithmetic operation of “VA−VN”. They can be associated withcharacteristics within a given less-than-90° angular range as shown inFIG. 23D. Therefore, by supplying these A.C. output signals to the phasedetection circuit 32, a phase angle θ within the less-than-90° angularrange in question can be detected in an absolute value. It should beunderstood that the above-mentioned dummy coil LN may be connected withthe detecting coil LA in parallel rather than in series as shown in FIG.23E. From a different point of view, the example of FIG. 23A can be saidto be a modification of the embodiment shown in FIGS. 1A-1C. Becauseonly one reference voltage VN is used, a narrower detectable phase anglerange is provided.

Whereas, in each of the above-described embodiments, the individualcoils in the coil section 10 are arranged coaxially and themagnetism-responsive member 11 is movable into the inner space definedby these coils, the present invention is not so limited and any desiredpositional relationship between the coil section 10 and themagnetism-responsive member 11 may be chosen. For example, as shown inFIG. 24, the coils Lα, LA-LD and Lβ in the coil section 10 may bedisposed such that their axes lie side by side along and themagnetism-responsive member 11 may be arranged to pass near therespective ends of the coils. In such a case, it is preferable that thecoils Lα, LA-LD and Lβ be each wound around an iron core.

Further, even in the case where the individual coils in the coil section10 are arranged coaxially as in the example of FIGS. 17A to 17C, themagnetism-responsive member 11 may be arranged to not move into theinner space defined by the coils, as shown by way of example in FIG.25A. In FIG. 25A, the magnetism-responsive member 11 is arranged to passnear the coils in parallel to their axes. In this case, it is preferablethat an iron core 53 be inserted through an axial inner space defined bythe coils Lα, LA-LD and Lβ. With such arrangements, a magnetic flux canflow out to the outer periphery of the coils with increased efficiency,which achieves an enhanced sensitivity to the magnetism-responsivemember 11 located close to the outer periphery of the coils and therebyenhances the detecting accuracy. FIG. 25A is a perspective view showingsuch a modification, where the magnetism-responsive member 11 is in theshape of a hollow cylindrical shape into which the coil section 10 ismovable. In this case too, it is preferable that an iron core 53 beinserted through an axial inner space defined by the coils Lα, LA-LD andLβ so that the magnetic flux can flow out to the outer periphery of thecoils with increased efficiency.

FIG. 26 is a schematic sectional side view showing other examples of thecoil section 10 and magnetism-responsive member 11. In this example, thecoils Lα, LA-LD and Lβ are spaced from each other with a pitch K as inthe example of FIGS. 17A and 17B, but each of the coils is smaller inlength than that in the example of FIGS. 17A and 17B. Namely, everyadjoining coils Lα, LA-LD and Lβ need not be so close to each other asin the example of FIGS. 17A and 17B and may be spaced from each other byany appropriate distance. The magnetism-responsive member 11 is tapered,over a length substantially equal to the coil length K, to have apointed tip 11 a. With the tapering over the length substantially equalto the coil length K, the inductance of each of the coils can increaseor decrease in a smooth progressive manner in response to a movement ofthe tip 11 a of the magnetism-responsive member 11. Of course, evenwhere the coils Lα, LA-LD and Lβ are located close to each other as inthe example of FIGS. 17A and 17B, the tip lla of themagnetism-responsive member 11 may be tapered as appropriate.

As a further example, each of the coils in the coil section 10 maycomprise a plurality of separate coil segments. FIG. 27 shows anexemplary arrangement of the separate coil segments, in which one coilLA is composed of four spaced-apart coil segments LA1, LA2, LA3 and LA4together covering the length of K. These coil segments LA1, LA2, LA3 andLA4 are connected in series with each other to produce abetween-terminal voltage VA of the coil LA. In this case, the coilsegments LA1, LA2, LA3 and LA4 may be either identical to or differentfrom each other in the number of coil turns. Further, the coil segmentsLA1, LA2, LA3 and LA4 may be spaced apart at uniform or non-uniformintervals as desired. By employing different numbers of coil turns andnon-uniform intervals between the coil segments (non-lineararrangements), there can be produced impedance variations withcharacteristics closer to a sine or cosine function curve, which canimprove the above-mentioned non-linearity between a detected phase angleθ and an actual distance (position) to be detected. Similarly, evenwhere the coils Lα, LA-LD and Lβ are located close to each other as inthe example of FIGS. 17A and 17B, the number of coil turns over thelength K of the coil in question may be made uniform or non-uniformbetween the coil segments. This also can produce impedance variationswith characteristics closer to a sine or cosine function curve, whichcan improve the above-mentioned non-linearity between a detected phaseangle θ and an actual distance (position) to be detected.

Further, the position detector device according to the present inventionis also applicable to detection of a position of an object to bedetected moving along an arcuate or curved path within a predeterminedrange, in addition to detection of a position of an object to bedetected moving along a completely linear path. FIG. 28 shows such anexample where the principles of the present invention are applied to thelinear position detection case. In FIG. 28, the coil section 10 includescoils LA-LD sequentially disposed arcuately over a predetermined angularrange ψ, and the magnetism-responsive member 11 is arranged to swingabout an axis C over the angular range ψ. Furthermore, the inventiveposition detector device can be constructed to detect an angle within apredetermined rotational angular range.

Note that in each of the above-described embodiments, themagnetism-responsive member 11 may be made of a non-magnetic substanceof good electrical conductivity, such as copper or aluminum, rather thana magnetic substance. In such a case, an eddy-current loss will causethe between-terminal voltage of the coil to progressively decrease asthe magnetism-responsive member 11 moves closer to the coil. Also notethat the magnetism-responsive member 11 may be of a hybrid typecomprising a combination of a magnetic substance and an electricallyconductive substance, in which case the magnetism-responsive member 11may be tapered to provide a tip 11 a of a non-magnetic andelectrically-conductive substance 11 b and a magnetic substance 11 c maybe provided to compensate for a shortage of the non-magnetic andelectrically-conductive substance 11 b due its tapered shape.

As still another example, the magnetism-responsive member 11 maycomprise a permanent magnet and each of the coils in the coil section 10may include an iron core, as illustratively shown in FIG. 30. In FIG.30, the permanent magnet 11M functioning as the magnetism-responsivemember 11 is in the shape of a ring into which the coil section 10 ismovable, and an iron core 54 is inserted through an axial inner spacedefined by the individual coils Lα, LA-LD and Lβ. When the permanentmagnet 11M gets close enough to any one of the coils, a portion of themagnetic core near the coil is magnetically saturated or supersaturated,so that the between-terminal voltage of the coil drops. The permanentmagnet 11M has a length at least equal to one coil length K in such amanner that the between-terminal voltage of the coil decreasesprogressively during a movement of the permanent magnet 11M from one endto the other of the coil. Namely, even in the case where the permanentmagnet 11M is used as the magnetism-responsive member 11, a progressivedecrease can be caused in the between-terminal voltage of the coilduring a movement of the permanent magnet 11M from one end to the otherof the coil, as in the case where the non-magnetic substance of goodelectrical conductivity 11 b is used. But, in the case of FIG. 30,non-saturated condition is restored once the permanent magnet 11M haspassed a given portion of the coil; however, the inventive positiondetector device may be constructed to provide output amplitude levelvariations of desired sine and cosine function characteristics byperforming appropriate analog arithmetic operations at a succeedingstage. Alternatively, the magnetically saturated or super-saturatedstate may be caused to persist by providing a succession of a pluralityof the permanent magnets 11M as the magnetism-responsive member 11. Thepermanent magnet 11M may have any other shape than a ring, such as arod, in which case the magnetism-responsive member 11 comprising thepermanent magnet 11M may be arranged to pass the neighborhood of thecoil section 10 in parallel to the axis of thereof. It is preferablethat the magnetic core 54 in this modification be formed into arelatively thin shape so that magnetic saturation takes place easily.

FIGS. 31A and 31B show modifications of the placement of the coils inthe coil section 10 of FIG. 25B, which is intended to prevent cross-talkbetween every adjoining coils and thereby enhance the detectingaccuracy. In the modification of FIG. 31A, the coils Lα, LA-LD and Lβare spaced from each other via magnetic spacers 62, so as to preventspreading of the magnetic flux produced from the individual coils,namely, the magnetic flux from each of the coils follows a path denotedat Φ in the figure, along which it flows out from the interior of thecoil, then passes a nearest end (i.e., the position of the magneticspacer 62), outer periphery of the coil and another nearest end (i.e.,the position of another magnetic spacer 62), and then returns to theinterior of the coil. Such arrangements effectively prevent theundesired cross-talk between the coils, which can greatly improveresponsiveness (impedance variations) of the individual coils withrespect to the presence of the magnetism-responsive member 11 movingclose to the outer periphery of the coils, thereby enhancing thedetecting accuracy. Whereas only one magnetic spacer 62 is disposedbetween every adjoining coils in the example of FIG. 31A, two magneticspacers 62, slightly spaced from each other, may be disposed betweenevery adjoining coils as illustrated in FIG. 31B. In the example of FIG.31B, a non-magnetic body may be used as a coil bobbin in place of themagnetic core 53. The idea of separating the coils from each other viathe magnetic spacers 62 a and 62 b as in the modifications of FIGS. 31Aand 31B is also applicable to the embodiment of FIG. 30.

FIG. 32 is a schematic axial sectional view showing still anotherembodiment of the position detector device of the present invention,which is arranged such that the coil inductance in the coil section 10progressively decreases as the magnetism-responsive member 11 movesdeeper into the coil section 10. FIG. 33A is a schematic perspectiveview showing a principal part of the detector device, showing anexemplary positional relationship between the coil section 10 and themagnetism-responsive member 11 of FIG. 32. FIG. 33B is a schematicsectional view taken along the axis of the coil section 10, and FIG. 33Cis a block diagram showing electric circuitry associated with the coilsection 10. In the position detector device of FIG. 32, themagnetism-responsive member 11 is in the shape of a hollow cylindricalshape into which the coil section 10 is movable, as in the examples ofFIGS. 25B and 30.

Further, in the embodiment of FIG. 32, the coil section 10 includes aplurality coils—in the illustrated example, four coils LA, LB, LC andLD—sequentially wound around a bobbin 70, and a non-magnetic andelectrically-non-conductive protective tube (which may alternatively bea coating or molding) 71 enclosing and thereby covering the outerperiphery of the plurality of coils. The protective tube 71 may beformed of any suitable material; however, a heat-shrinkable protectivetube made of insulating resin is most preferable because of its lowcost.

The bobbin 70 is in the form of a non-magnetic hollow cylinder, in whichis received one or more magnetic rods 72. The rods 72 extend throughoutthe length of the coil section 10 and act to set an inductance value,i.e., impedance, along the entire length of the coil section 10. Thesetting of such an inductance value along the entire length of the coilsection 10 can be changed as desired by appropriately adjusting thethickness and the number of the rods 72 received within the bobbin 70.Preferably, each of the magnetic rods 72 is plated with copper or thelike to provide a conductive coating on its peripheral surface so thatthe conductive coating helps to compensate temperature driftcharacteristics. The bobbin 70 may be formed of any suitable metal orresin as long as it is non-magnetic. In cases where an apparatusemploying the inventive position detector device is applied to largeconstruction machinery or the like that is subjected to great loads, itis more preferable that the bobbin 70 be formed of metal, such asnon-magnetic stainless steel, to assure a sufficient mechanicalstrength. In application to small-size equipment or apparatus, however,the bobbin 70 had better be formed of resin because of its lower costand weight.

The following paragraphs describe how the position detector device ofFIG. 32 operates for position detection, with reference to FIGS. 33A to33C. Note that in FIGS. 33A to 33C, only one magnetic rod 72 is shownand the. bobbin 70 is not shown, for simplicity of illustration.

In the coil section 10 of FIGS. 33A to 33C, the coils LA, LB, LC and LD,which are equal to each other in the number of coil turns, coil lengthand various other characteristics, are placed in series along thedirection in which the object to be detected is caused to move linearly.In this embodiment, the relative positions between the coil section 10and the magnetism-responsive member 11 vary in response to displacementof the object to be detected in a similar manner to the embodiment ofFIGS. 17A and 17B. More specifically, when the magnetism-responsivemember 11 moves toward the rear end of the coil section 10, namely,rightward in the figure, in response to displacement of the object to bedetected, the tip lla of the magnetism-responsive member 11 first entersa magnetic field of the leading coil LA and then enters respectivemagnetic fields of the other coils LB, LC and LD sequentially in theorder mentioned. A dot-and-dash line 11′ in FIG. 33B depicts themagnetism-responsive member 11 having completely entered as far as themagnetic field of the last coil LD. Axial range 4K (4×K) correspondingto the four coils LA, LB, LC and LD together constitute the effectivedetecting range of the position detector device. However, because thedetecting accuracy, in effect, tends to fall to some degree at oppositeends of the axial ranges 4K, the opposite ends of the effectivedetecting range are not actually used for the position detectionpurposes, so that the effective detecting range would become slightlyshorter than a total length of the axial ranges 4K. Of course, in orderto permit accurate detection along the full length of the effectivedetecting range, auxiliary coils Lα and Lβ may be provided immediatelybefore and after the effective detecting range 4K in a similar manner tothe above-described embodiments.

The one or more magnetic rods 72 extend axially through the individualcoils LA, LB, LC and LD at their respective core regions. The one ormore magnetic rods 72 present a maximum inductance value unless themagnetism-responsive member 11 is located sufficiently close to the coilsection 10. As the magnetism-responsive member 11 moves closer to orfurther into the magnetic field of any one of the coils, theself-inductance of the coil decreases; thus, a voltage between oppositeends of the coil decreases progressively as the tip 11 a of themagnetism-responsive member 11 is displaced from one end to the other ofthe coil in question. More specifically, in the case where themagnetism-responsive member 11 is formed of a magnetic substance, themagnetic substance covers the outer periphery of the coil which has cometo be surrounded by the magnetism-responsive member 11 and thus amagnetic flux, having so far concentrated solely at the magnetic cores,namely, the rods 72, in the coil core region, leaks out to the member11, so that the self-inductance of the coil is caused to decrease.Further, in the case where the magnetism-responsive member 11 is formedof an electrically-conductive substance, the conductive substance coversthe outer periphery of the coil which has come to be surrounded by themember 11 and thus an eddy-current loss occurs due to the magneticfield, which also causes the self-inductance of the coil to decrease.That is, in the embodiment of FIG. 32, the self-inductance of each ofthe coils which have come to be surrounded by the member 11 is caused todecrease as the magnetism-responsive member 11 moves closer to orfurther into the magnetic field of the coil section 10, irrespective ofwhether the member 11 is formed of magnetic substance orelectrically-conductive substance. However, the use of theelectrically-conductive substance as the magnetism-responsive member 11is more preferable because the rate of the inductance decrease caused bythe eddy-current loss in the coil-surrounding conductive substance isgreater that the rate of the inductance decrease caused by the magneticflux leakage to the coil-surrounding magnetic substance. Because it isonly necessary that the electrically-conductive substance produce aso-called “skin effect”, the substance may be in the form of a just thinlayer provided on the magnetism-responsive member 11. In such a case,the magnetism-responsive member 11 may be formed such as by providing anelectrically-conductive substance (e.g., copper plating) on and along aninner wall surface of a suitable base member (mobile member) having ahollow cylindrical shape.

As shown in FIG. 33C, the individual coils LA, LB, LC and LD areexcited, at a constant voltage or current, by a predeterminedsingle-phase A.C. signal (“sin ωt”) generated by the A.C. power supply30. Voltages between the respective opposite ends of these coils LA, LB,LC and LD are denoted in the figure by “VA”, “VB”, “VC” and “VD”,respectively, and taps 14-18 are provided to take out these voltages VA,VB, VC and VD. As may be readily understood, the coils LA, LB, LC and LDneed not necessarily be physically-separated coils, and they may bereplaced by just a single continuous coil divided into four lengths orcoil portions by the intermediate taps 14-18; that is, the coil portionbetween the taps 14 and 15 functions as the coil LA, the coil portionbetween the taps 15 and 16 functions as the coil LB, the coil portionbetween the taps 16 and 17 functions as the coil LC and the coil portionbetween the taps 17 and 18 functions as the coil LD. Output voltages VA,VB, VC and VD from the individual coils are delivered, in predeterminedcombinations, to the analog arithmetic operation circuits 311 and 312,in which they are subjected to an addition and/or subtraction based onpredetermined mathematical expressions as will be later described. Thus,these analog arithmetic operation circuits 311 and 312 produce two A.C.output signals sin θ sin ωt and cos θ sin ωt of amplitudes that presentsine and cosine function characteristics corresponding to a currentposition of the object to be detected.

As mentioned earlier, as the magnetism-responsive member 11 moves closerto or further into the magnetic field of each of the coils, theself-inductance of the coil decreases, and thus the voltage between theopposite ends of the coil decreases progressively during displacement ofthe tip 11 a of the member 11 from one end to the other of the coil.Here, because the coils LA, LB, LC and LD are placed in series along thedisplacement direction of the to-be-detected object, progressivevariations in the respective voltages VA, VB, VC and VD of the coils LA,LB, LC and LD will occur sequentially, as illustratively shown in part(A) of FIG. 34, as the magnetism-responsive member 11 moves relative tothe coils LA, LB, LC and LD in response to the displacement of theobject to be detected. In part (A) of FIG. 34, a slope in each of thecurves, indicative of the output voltages VA, VB, VC and VD from thecoils LA, LB, LC and LD, represents a region where the tip 11 a of themagnetism-responsive member 11 is moving from one end toward the otherof the coil in question. Typically, a progressive variation curve of thevoltage between the opposite ends of the coil, which takes place duringthe movement of the magnetism-responsive member 11 from the coil's oneend to the other, can be likened to a functional value variation withina 90° range of the sine or cosine function. Thus, by appropriatelycombining the output voltages VA, VB, VC and VD from the individualcoils LA, LB, LC and LD and performing an addition and/or subtractionbetween the combinations, it is possible to produce two A.C. outputsignals sin θ sin ωt and cos θ sin ωt of amplitudes that present sineand cosine function characteristics corresponding to a current positionof the object to be detected.

More specifically, the analog arithmetic operation circuit 311 canprovide an A.C. output signal indicative of an amplitude curve of thesine function characteristic as shown in part (B) of FIG. 34, byperforming arithmetic operations on the output voltages VA, VB, VC andVD from the coils LA, LB, LC and LD in accordance with Expression (10)below; the A.C. output signal can be represented equivalently by “sin θsin ωt”.

(VB−VA)−(VD−VC)−Vo  Expression (10)

Note that “Vo” represents a reference voltage corresponding to a minimuminductance value obtained when the magnetism-responsive member 11 hascovered the entirety of one of the coils and this reference voltage isused here to offset the output voltage to a zero level.

Further, the other analog arithmetic operation circuit 312 can providean A.C. output signal indicative of an amplitude curve of the cosinefunction characteristic as shown in part (B) of FIG. 34, by performingarithmetic operations on the output voltages VA, VB, VC and VD from thecoils LA, LB, LC and LD in accordance with Expression (11) below; theA.C. output signal can be represented equivalently by “cos θ sin ωt”.

VA+(VB−VC)+(Vp−VD)−Vo  Expression (11)

Note that “Vp” represents a reference voltage corresponding to a maximuminductance value obtained when the magnetism-responsive member 11 is notlocated sufficiently close to any one of the coils and this referencevoltage is used here to offset the output voltage VD. Consideringtemperature drifts, generation of the reference voltages Vo and Vp hadbetter be carried out using a suitable dummy coil so that these voltagesVo and Vp may be generated with the same temperature driftcharacteristics as those of the coils LA, LB, LC and LD. However, anyother suitable temperature compensation means may of course be employed.

Phase angle θ in the sine and cosine functions, which are amplitudecomponents of the individual A.C. output signals, corresponds to thecurrent position to be detected, and a phase angle θ within the 90°range corresponds to the length of one of the coils. Thus, the effectivedetecting range of the 4K length corresponds to phase angles e rangingfrom 0° to 360°. Therefore, every position within the effectivedetecting range of the 4K length can be detected in an absolute value bydetecting such a phase angle θ. Specifically, in a similar manner to theabove-mentioned, every position within the effective detecting range canbe detected in an absolute value by means of the phase detection circuit(or amplitude-to-phase converting means) 32 which detects the phasecomponent e of the amplitude functions sin θ and cos θ in the A.C.output signals sin θ sin ωt and cos θ sin ωt of the sine and cosinefunction characteristics.

Now, an explanation is given below about compensation of the temperaturecharacteristics in the embodiment of FIG. 32. Impedance of theindividual coils varies with a change in temperature, and such animpedance variation results in variations in the output voltages VA, VB,VC and VD from the individual coils. For example, as illustrated in part(A) of FIG. 34, each of the output voltages VA, VB, VC and VD would varyto increase or decrease in one direction, relative to a solid-linecurve, as depicted by dotted line, as in the case of FIG. 18. However,in the A.C. output signals sin θ sin ωt and cos θ sin ωt of the sine andcosine function characteristics, obtained by the additive andsubtractive syntheses of the output voltages, the variations wouldappear as positive and negative amplitude variations as shown by dottedlines in contradistinction with solid-line curves in part (B) of FIG.34. This means that compensation of the temperature driftcharacteristics has been duly achieved without influencing the phaseangle θ in the individual sine and cosine functions, and thushigh-accuracy position detection can be provided by the positiondetector device. Further, the temperature drift compensation can be madeby forming a conductive coating, such as copper plating, on the outerperiphery of each of the magnetic rods 72 functioning as the magneticcores of the coil section 10, as set forth above. More specifically,although the conductive coatings on the magnetic rods 72 act to reducethe inductance of the magnetic circuit due to the eddy-current lossgenerated therein, the eddy-current loss in the conductive coatingsdecreases to cause the inductance of the magnetic circuit to increaserelatively as the coil impedance increases, for example, in response toa temperature increase, which thus can compensate for the temperaturedrifts of the coil inductance. For the same reasons, a similartemperature drift compensation effect can be provided by using a more orless conductive substance as the non-magnetic metal of the bobbin 70.

Although each of the embodiments has been described above as generatingtwo A.C. output signals sin θ sin ωt and cos θ sin ωt having amplitudecharacteristics of sine and cosine functions (so to speak, resolver-typetwo-phase outputs), the present invention is not so limited and may bedesigned to generate three or more A.C. output signals having amplitudecharacteristics of three or more trigonometric functions phase-shiftedby a predetermined amount (e.g., sin θ·sin ωt, sin(θ−120°)·sin ωt andsin(θ−240°)·sin ωt). Further, the number of the coils LA-LD may begreater than four.

Further, as shown in FIG. 35, two groups of coils Lα, LA-LD, Lβ and Lα′,LA′-LD′, Lβ′ (or three or more groups of coils) may be provided inparallel while positionally deviating from each other by a predetermineddistance d, in which case the magnetism-responsive member 11 is formedinto a size sufficient to cover all the coil groups. The coils in allthese groups are excited by a same-phase A.C. signal (e.g., sin ωt). Thedeviation of distance b results in an appropriate phase difference lessthan 90°, and thus a plurality of A.C. output signals presentingamplitudes based on a plurality of trigonometric functions which havenon-90° phase differences (trigonometric functions in other than thesine/cosine relationship), such as sin θ·sin ωt, sin(θ−120°)·sin ωt andsin(θ−240°)·sin ωt, can be generated by combining the output voltages ofthese coils after performing appropriate addition and/or subtractionoperations thereon.

As a further modification of the present invention, only one of theanalog arithmetic operation circuits 311 of FIG. 17C may be used togenerate only one A.C. output signal sin θ·sin ωt. In such amodification, position detecting data will be obtained from theamplitude voltage level of the only A.C. output signal sin θ·sin ωtwithout using the phase detection circuit 32. In this case too, therecan be provided a simplified position detector device equipped with nosecondary coil.

It should also be noted that a position detector device based on theknown phase-shift-type phase detection principles can be constructed bycombining a pair of the position detector devices capable of generatingonly one A.C. output signal sin θ·sin ωt in the same manner as theabove-described modification. Namely, in such a position detector devicebased on the known phase-shift-type phase detection principles,plural-phase primary coils are excited by two-phase A.C. signals (e.g.,sin ωt and cos ωt), and an A.C. output signal (e.g., sin(ωt+θ)),phase-shifted by a phase angle θ corresponding to a current position ofthe object to be detected, can be produced as a composite of the outputsignals of the individual phases. The idea of the present invention maybe applied to such a position detector device based on the knownphase-shift-type phase detection principles. For that purpose, two coilgroups may be provided in parallel and the coils in each of the groupsmay be excited by A.C. signals of different phases (e.g., sin ωt and cosωt) in such a way that one of the coil groups outputs sin θ cos ωt whilethe other coil group outputs sin θ sin ωt and an addition or subtractionis performed on these two outputs.

It should also be obvious that the magnetism-responsive member 11 ineach of the embodiments shown in FIGS. 17A to 35 may be fixed while thecoil section 10 is arranged to move linearly relative to themagnetism-responsive member 11 in response to displacement of the objectto be detected.

The position detector device employing a permanent magnet as shown inFIGS. 6 and 30 is also applicable to an application where the coilsection includes primary and secondary coils, as illustratively shown inFIG. 36. Specifically, FIG. 36 is a partly-sectional schematic view of alinear-type position detector device in accordance with anotherembodiment of the present invention. This linear-type position detectordevice 80 basically comprises an iron core 82, and a coil section 81wound around the iron core 82 in predetermined conditions, and apermanent magnet section 90 movable relative to the coil section 81. Theiron core 82 is preferably formed of silicon steel having a highmagnetic permeability and low coercive force. However, the iron core 82may be formed of any other suitable material than silicon steel, or maycomprise a lamination of silicon steel plates formed into a rectangularparallelopiped. Further, the iron core 82 may be in any desired shape.The coil section 81 includes a plurality of primary coils P1-P5 to beexcited by a predetermined A.C. signal, and a plurality of secondarycoils S1-S4 wound to assume a predetermined positional relationship in apredetermined direction X.

FIG. 37 is a diagram showing connections of the primary coils P1-P5 andsecondary coils S1-S4. As seen from the figure, the primary coils P1-P5only have to be excited by a same single-phase A.C. signal (e.g., sinωt); only one or any desired plurality of the primary coils may beprovided in any desired placement. The secondary coils S1 and S3 areconnected to operate in a differential manner; so are the secondarycoils S2 and S4.

In a situation where a mechanical system whose position is to bedetected by the position detector device 80 is a linear motor, the coilsection 81 is connected with a moving member (not shown) of the linearmotor so that it is movable linearly and in a reciprocative fashion inresponse to a changing linear position of the moving member. In thisembodiment, the permanent magnet section 90 functions as a railroad forthe linear motor. Namely, the linear motor is constructed in such a waythat the moving member moves over a railroad, i.e., permanent magnetsection 90 made up of a series of magnets 91, 92, . . . as shown in FIG.36. Of course, the relationship between the moving member and thepermanent magnet section 90 may be reversed whenever desired. Referringto the magnets 91 and 92, for example, a magnetic flux is dense in aconnection between the magnets 91 and 92 while the magnetic flux issparse in and around respective middle regions of these magnets 91 and92. Therefore, regions of dense and sparse magnetic flux occuralternately on the railroad 90 with predetermined pitches P.

If pitches of alternate placement of N and S poles of the magnets 91,92, . . . are denoted by P, the secondary coils S1-S4 are placed, forexample, in the following positional relationship. The secondary coil S3is spaced from the secondary coil S1 by a distance equal to an integralmultiple of half the pitch P(P/2) (namely, S3=S1+(P/2+nP)), thesecondary coil S2 is spaced from the secondary coil S1 by a distanceequal to an integral multiple of a quarter of the pitch P(P/4) (namely,S2=S1+(P/4+nP)), and the secondary coil S4 is spaced from the secondarycoil S2 by a distance equal to an integral multiple of half the pitchP(P/2) (namely, S4=S1+(P/2+nP)). With such a positional relationship,the secondary coil S1 presents a characteristic of sine function (sin),the secondary coil S3 presents a characteristic of minus sine function(−sin), the secondary coil S2 presents a characteristic of cosinefunction (cos), and the secondary coil S4 presents a characteristic ofminus cosine function (−cos).

In response to a changing linear position of the moving member to bedetected, i.e., the coil section 81, the dense and sparse magnetic fluxregions of the railroad, i.e., the permanent magnet 90, alternately acton the coil section 81. More specifically, when any one of the secondarycoil faces one of the dense magnetic flux regions, the magnetic fluxfrom the magnet passes a corresponding portion of the iron core 82densely, so that a magnetic coupling force of that secondary coil to theadjoining primary coils would be weakened. This is because the magneticflux passing the iron core 82 becomes dense due to the magnetic fluxfrom the magnet to thereby produce magnetic saturation in thecorresponding portion of the iron core 82 and thus there occurs suchmagnetic coupling just as in “coreless” condition where no iron coreexists. Therefore, when the secondary coil faces the connection betweenthe magnets 91 and 92 where the magnetic flux is dense, a secondaryelectromotive force becomes weakest. When, on the other hand, thesecondary coil faces one of the sparse magnetic flux regions, themagnetic flux from the magnet passes a corresponding portion of the ironcore 82 sparsely, so that a magnetic coupling force of that secondarycoil to the adjoining primary coils would not change so much.

Thus, A.C. output signals induced in the individual secondary coils arecaused to vary in response to a variation in the relative linearpositions between the coil section 81 and the railroad, i.e., thepermanent magnet 90. Namely, inductive A.C. output signalsamplitude-modulated in accordance with a relative linear position of themoving member, i.e., the object to be detected, are produced, from theindividual secondary coils S1-S4, with amplitude functioncharacteristics differing in correspondence with the respectivepositions of the secondary coils S1-S4. As the primary coils P1-P5 areexcited by the same single-phase A.C. signal sin ωt as shown in FIG. 2,the inductive A.C. output signals produced from the individual secondarycoils S1-S4 are caused to change in cycles with each of the cyclesrepresenting a variation amount that has a same electrical phase andamplitude function corresponding to the pitch P of the dense and sparsemagnetic flux regions of the magnets 91 and 92.

Inductive voltage levels of the secondary coils S1-S4 present two-phasepositive function characteristics sin θ and cos θ and negative or minusversions of the function characteristics −sin θ and −cos θ correspondingto a linear position of the object to be detected. Namely, the inductiveoutput signals from the secondary coils S1-S4 are provided after havingbeen amplitude-modulated with the two-phase positive functioncharacteristics sin θ and cos θ and negative function characteristics−sin θ and −cos θ corresponding to a current linear position of theobject to be detected. Note that “θ” is proportional to a linearposition “x” so as to provide, for example, a relationship of θ=2π(X/P). For convenience of description, the number of coil turns andcoefficients corresponding to other conditions are not considered andalso let it be assumed that the secondary coil S1 is of the sine phase,the secondary coil S2 is of the co sine phase, the secondary coil S3 isof the minus sine phase and the secondary coil S4 is of the minus cosinephase. By differentially synthesizing the inductive outputs of the sineand minus sine phases, there can be generated a first A.C. output signal(sin θ*sin ωt) having an amplitude function of the sine function.Similarly, by differentially synthesizing the inductive outputs of thecosine and minus cosine phases, there can be generated a second A.C.output signal (cos θ*sin ωt) having an amplitude function of the cosinefunction.

In this way, there are provided a first A.C. output signal A (=sin θ*sinωt) having an amplitude value of a first function value sin θcorresponding to a current linear position of the object to be detected,and a second A.C. output signal B (=cos θ*sin ωt) having an amplitudevalue of a second function value corresponding to the linear position ofthe object to be detected. With such wiring, the linear-type positiondetector device can provide two same-phase A.C. output signals havingtwo-phase amplitude functions (sine and cosine outputs), in a similarmanner to the conventional resolvers that are among the rotary-typeposition detector devices.

In summary, the described invention can provide an improved positiondetector device which is very compact in size and very simple instructure, because it requires only primary coils with no need for asecondary coil. Further, using a combination of one coil and tworeference voltages or a combination of two coils and one referencevoltage, the present invention can readily produce a plurality of A.C.output signals presenting amplitudes of predetermined cyclic functioncharacteristics (e.g., two A.C. output signals presenting amplitudes ofsine and cosine function characteristics), in response to a currentlinear position of an object to be detected, and also can allocate atleast about one quadrant (90°) range as an available phase angle range.Thus, even with a reduced number of coils, the described invention iscapable of position detection over a relatively wide phase angle rangeand achieves an enhanced detecting resolution. Further, even for veryminute or microscopic displacement of the object to be detected, aposition of the object can be detected with a high resolution.Furthermore, if a circuit (e.g., a coil) presenting temperaturecharacteristics similar to those of detecting coils is employed as thecircuit for generating a reference voltage, subtractive arithmeticoperations in arithmetic operation circuitry can automaticallycompensate for the temperature drifts, thereby providing forhigh-accuracy position detection without influences of a temperaturechange.

Furthermore, the described invention can provide an improved rotary-typeposition detector device which is very compact in size and very simplein structure, because it requires only primary coils with no need for asecondary coil. In addition, by performing arithmetic operations on anoutput signal from one coil and the reference voltage, there can begenerated an output signal presenting amplitude coefficientcharacteristics of a real sine or cosine function with amplitudecoefficient components swinging in the positive and negative directions,with the result that the present invention can significantly simplifythe coil structure to thereby provide a more sophisticated rotary-typeposition detector device of an even smaller size and an even furthersimplified structure.

Moreover, with the arrangement that a plurality of coil segments areplaced in series along a displacement direction of an object to bedetected so that progressive incremental or decremental variations inthe respective between-terminal voltages of the coil segments occursequentially as the magnetism-responsive member moves relative to thecoil segments in response to the displacement of the object to bedetected, the present invention can produce a plurality of A.C. outputsignals presenting amplitudes of predetermined cyclic functioncharacteristics (e.g., two A.C. output signals of sine and cosinefunction characteristics) corresponding to a current position of theobject, by appropriately combining the voltages taken out from the coilsegments after performing an addition and/or subtraction on thevoltages. In addition, even for very minute or microscopic displacementof the object to be detected, a position of the object can be detectedwith a high resolution, by detecting, from a correlation between theamplitude values of these A.C. output signals, a phase value in thepredetermined cyclic functions (e.g., sine and cosine functions)defining the amplitude values.

Finally, further embodiments of the present invention will be describedhereinbelow.

FIG. 38A is a schematic perspective view of a position detector device,where the coil section 50 includes only one coil L1 and a positiondetection signal using a combination of an output voltage Vx from thecoil L1 and two reference voltages Va and Vb in a similar manner to theembodiment of FIG. 1. FIG. 38B is a partly-sectional side view of theposition detector device shown in FIG. 38A. Magnetism-responsive member65 is provided on a base member 66 shaped like a rod, such as a cylinderpiston rod; specifically, the magnetism-responsive member 65 comprises apattern of a predetermined progressively-increasing orprogressively-decreasing shape, such as a triangle, which is formed on asurface of the rod-shaped base member 66. The magnetism-responsivemember 65 and base member 66 are made of substances having differentmagnetic characteristics. If the base member 66 is made of a magneticsubstance such as iron, the magnetism-responsive member 65 is made of anon-magnetic substance of good electrical conductivity such as copper.Or, if the magnetism-responsive member 65 is made of a magneticsubstance such as iron, then the base member 66 is made of anon-magnetic substance or magnetic substance having a concave profilecorresponding to the magnetism-responsive member 65 formed into a convexshape. As shown in FIG. 38B, the coil L1 is inserted in a U-shapedinterior space defined by a magnetic core 52 in the form of a ringhaving a U-shaped section, and the rod-shaped base member 66 providedwith the magnetism-responsive member 65 is inserted in a ring-shapedinner space defined by the coil L1 in such a manner that the coil LI islinearly movable in the axial direction thereof. Magnetic path Φ of thecoil L1 passes the surface of the rod-shaped base member 66 in arelatively great amount. In this embodiment, the length of the coil L1has no relation to the detection range K and may be short and simple.Range K of the progressively-increasing or progressively-decreasingpattern of the magnetism-responsive member 65, provided on the basemember 66, corresponds to the detectable range K. Namely, as therod-shaped base member 66 moves in response to displacement of theobject to be detected, the position of the magnetism-responsive member65 corresponding to the coil L1 changes, so that there is produced, inthe coil L1, a self-inductance, i.e., impedance, corresponding to anarea of the member 65 corresponding to (traversing) the coil L1 and anoutput voltage Vx corresponding to a current position of the object tobe detected is produced from the coil L1. FIG. 38C shows an example ofthe pattern of the magnetism-responsive member 65 which is formed on thesurface of the rod-shaped base member 66. This pattern may be either asingle pattern or a plurality of similarly-shaped patterns placed sideby side.

Electric circuitry applied to the embodiment of FIGS. 38A-38C may be ofthe same construction as the one shown in FIG. 1C, and essentialbehavior of the embodiment may be similar to the one described earlierin relation to FIGS. 2A and 2B. Further, the modification where aplurality of coils are used as shown in FIGS. 7A and 7B, themodification where a single reference voltage VN is used as shown inFIG. 23A, or the modification where a reference voltage VR variable inresponse to displacement x via a resistor element is used as shown inFIG. 22A is also applicable to the embodiment of FIGS. 38A-38C.

FIGS. 39A-39E and FIGS. 40A-40D are schematic views of position detectordevices in accordance with still other embodiments of the presentinvention, where the coil section 10 includes a plurality of coils LA,LB, . . . and two-phase, sine and cosine, detection output signals(typically, sin θ sin ωt and cos θ sin ωt) corresponding to a currentposition of an object to be detected are generated using combinations ofoutput voltages VA, VB, . . . from these coils, in a similar manner toother embodiments such as the embodiments of FIGS. 17A, 17B, 21A, 33Aand 33B. In these embodiments, similarly to the embodiment of FIGS. 38Aand 38B, magnetism-responsive members 11 a, 11 b, . . . are formed onthe rod-shaped base member 66; specifically, each of themagnetism-responsive members 11 a, 11 b, . . . comprises a pattern of apredetermined progressively-increasing or progressively-decreasingshape, which is formed on a surface of the rod-shaped base member 66.These embodiments are different from the embodiment of FIGS. 38A and 38Bin that the patterns of the magnetism-responsive members 11 a, 11 b, . .. differ from each other as appropriate and separate coils L1, L2, . . .are provided in corresponding relation to the patterns. Variouscombinations of the substances forming these magnetism-responsivemembers 11 a, 11 b, . . . and base member 66 may be chosen in the samemanner as with the embodiment of FIGS. 38A and 38B.

FIG. 39A is a cross-sectional view showing the rod-shaped base member 66and coil section 10. The coil section 10 is generally in the shape of aring, in which the rod-shaped base member 66 is inserted for linearmovement in the axial direction thereof. The first coil L1 is positionedin one half portion of the coil section 10 and the second coil L2 ispositioned in the other one half portion of the coil section 10. FIG.39B is a view showing the rod-shaped base member 66 and coil section 10in an unfolded condition, where arrow x indicates a direction of lineardisplacement of the object to be detected. As shown, themagnetism-responsive members 11 a and 11 b comprise two separatepatterns; that is, the first pattern 11 a is a triangle progressivelyincreasing or widening in a left-to-right direction while the secondpattern 11 b is a triangle progressively decreasing or narrowing in theleft-to-right direction. The first coil L1 covers the positioned area ofthe pattern 11 a. The second coil L2 covers the positioned area of thepattern 11 b.

FIG. 39C is a block diagram of electric circuitry associated with theindividual coils L1 and L2 of FIG. 39A, and FIGS. 39D end 39E arediagrams explanatory of position detecting operation of the embodiment.Similarly to the above-mentioned, as the rod-shaped base member 66 movesin response to displacement of the object to be detected, the positionsof the magnetism-responsive members 11 a and 11 b corresponding to thecoils L1 and L2 change, so that there is produced, in the coils L1 andL2, self-inductance, i.e., impedance, corresponding to areas of themembers 11 a and 11 b corresponding to the coils L1 and L2 and outputvoltages Va and Vb corresponding to a current position of the object tobe detected are produced from the coils L1 and L2. These output voltagesVa and Vb present opposite characteristics as shown in FIG. 39D.Therefore, variations in these output voltages Va and Vb can each belikened to a function value variation within an appropriateless-than-90° range in a sine or cosine function. Thus, by extractingthese output voltages Va and Vb by means of an appropriate analog buffercircuit 100, there can be generated two A.C. output signals (typically,sin θ sin ωt and cos θ sin ωt) having amplitudes presenting sine andcosine functional characteristics corresponding to a current position ofthe object to be detected.

FIGS. 40A-40D show the embodiment which can realize a full phasevariation from a substantially zero degree to 360 degrees. Morespecifically, FIG. 40A is a diagram showing, in an unfolded condition,four different patterns 11 a, 11 b, 11 c and 11 d that are formed on thebase member 66 by the magnetism-responsive member 11. These patterns 11a, 11 b, 11 c and 11 d are positioned in corresponding relation to fourregions of a peripheral surface of the rod-shaped base member 66 whichare divided circumferentially along the peripheral surface. Forconvenience of description, the rod-shaped base member 66 is shown inpart (a) of the figure as being divided into four portions along thelength thereof, and these divided portions are denoted by P1, P2, P3 andP4, respectively. For example, the pattern 11 a is a triangleprogressively increasing in area or widening in the left-to-rightdirection over the portion P1 but progressively decreasing or narrowingin the left-to-right direction over the portion P4. In each of theportions P2 and P3, the pattern 11 a covers the whole area, i.e., whollyfunctions as the magnetism-responsive member 11. The other patternsdiffer from each other in a sequential manner as shown.

Further, FIG. 40B is a diagram showing progressively-increasing andprogressively-decreasing variations in output voltages V1-V4. FIG. 40Dis a block diagram of electric circuitry associated with the individualcoils L1-L4, where an analog arithmetic operation circuit 101 performsarithmetic operations of “V1-V3” and “V2-V4”. FIG. 40C is a graphshowing an output signal provided as a result of the arithmeticoperations. The voltage “V1-V3” obtained by subtracting the outputvoltage V3 from the voltage V1 can be likened to a sine functioncharacteristic falling within a range from a substantially zero degreeto 360 degrees. On the other hand, the voltage “V2-V4” obtained bysubtracting the output voltage V4 from the voltage V2 can be likened toa cosine function characteristic falling within a range from asubstantially zero degree to 360 degrees. Therefore, there can begenerated signals to A.C. output signals (typically, sin θ sin ωt andcos θ sin ωt) having sine and cosine functional characteristics over thesubstantially 360° range.

It should be obvious that the base member 66 may be in any othersuitable shape than a rod, such as a flat plate, in which case the coilsL1, L2, . . . are placed in opposed relation to the magnetism-responsivemembers 11, 11 a, 11 b, . . . formed on the plate.

What is claimed is:
 1. A position detector device comprising: a coilsection including at least one coil to be excited by an A.C. signal; amagnetism-responsive member movable relative to said coil section,wherein relative positions between said magnetism-responsive member andsaid coil section vary in response to displacement of an object to bedetected and impedance of said coil is caused to vary in response to avariation in the relative positions in such a manner that a voltageproduced in said coil is caused to vary in response to a variation inthe impedance of said coil during the variation in the relativepositions within a predetermined range; a reference-voltage generationcircuit adapted to generate at least one predetermined reference voltagein the form of an A.C. signal; and an arithmetic operation circuitcoupled to said coil and reference-voltage generation circuit, saidarithmetic operation circuit adapted to perform an arithmetic operationbetween said voltage produced in said coil and said predeterminedreference voltage, so as to generate at least two A.C. output signalshaving predetermined cyclic amplitude functions as amplitudecoefficients, the cyclic amplitude functions of the two A.C. outputsignals being different, in their cyclic characteristics, from eachother by a predetermined phase.
 2. A position detector device as claimedin claim 1 wherein said coil section includes a single coil, saidreference-voltage generation circuit generates first and secondreference voltages, and said arithmetic operation circuit performspredetermined first and second arithmetic operations using a voltageproduced in said single coil and said first and second referencevoltages, to thereby generate a first A.C. output signal having a firstamplitude function as an amplitude coefficient and a second A.C. outputsignal having a second amplitude function as an amplitude coefficient.3. A position detector device as claimed in claim 2 wherein said firstand second reference voltages define specific phase sections in cycliccharacteristics of said first and second amplitude functions of saidfirst and second A.C. output signals, and wherein correspondence betweenthe specific phase sections and a variation range of the relativepositions can be varied by varying said first and second referencevoltages.
 4. A position detector device as claimed in claim 1 whereinsaid reference-voltage generation circuit includes a coil ofpredetermined impedance which is positioned so as not to be influencedby a movement of said magnetism-responsive member.
 5. A positiondetector device as claimed in claim 1 wherein said coil includes amagnetic core and said magnetism-responsive member has a flat surfacethat is opposed to said magnetic core of said coil with an air gapinterposed therebetween, and wherein as the flat surface of saidmagnetism-responsive member moves in response to a changing position ofthe object to be detected, there occurs a dimensional variation in theair gap which brings about a variation in the impedance of said coil. 6.A position detector device as claimed in claim 1 wherein said coilincludes a magnetic core, and the impedance of said coil is caused tovary as a distance defined by an air gap between said magnetic core andsaid magnetism-responsive member or an area of the air gap varies inresponse to a changing position of the object to be detected.
 7. Aposition detector device as claimed in claim 2 wherein said first andsecond amplitude functions are sine and cosine functions, respectively.8. A position detector device as claimed in claim 1 wherein saidmagnetism-responsive member includes at least one of a magneticsubstance and an electrically-conductive substance.